innerText IDL attributebody elementarticle elementsection elementnav elementaside elementh1, h2, h3, h4, h5, and
h6 elementshgroup elementheader elementfooter elementaddress elementp elementhr elementpre elementblockquote elementol elementul elementmenu elementli elementdl elementdt elementdd elementfigure elementfigcaption elementmain elementdiv elementa elementem elementstrong elementsmall elements elementcite elementq elementdfn elementabbr elementruby elementrt elementrp elementdata elementtime elementcode elementvar elementsamp elementkbd elementsub and
sup elementsi elementb elementu elementmark elementbdi elementbdo elementspan elementbr elementwbr elementa and area elementsa and area elementsalternate"author"bookmark"canonical"dns-prefetch"external"help"icon"license"modulepreload"nofollow"noopener"noreferrer"opener"pingback"preconnect"prefetch"preload"prerender"search"stylesheet"tag"picture elementsource elementimg elementsource,
img, and link elementsiframe elementembed elementobject elementparam elementvideo elementaudio elementtrack elementTrackEvent interfacemap elementarea elementtable elementcaption elementcolgroup elementcol elementtbody elementthead elementtfoot elementtr elementtd elementth elementtd and th elementsform elementlabel elementinput elementtype attributetype=hidden)type=text) state and Search state (type=search)type=tel)type=url)type=email)type=password)type=date)type=month)type=week)type=time)type=datetime-local)type=number)type=range)type=color)type=checkbox)type=radio)type=file)type=submit)type=image)type=reset)type=button)input element attributesmaxlength and minlength attributessize attributereadonly attributerequired attributemultiple attributepattern attributemin and max attributesstep attributelist attributeplaceholder attributeinput element APIsbutton elementselect elementdatalist elementoptgroup elementoption elementtextarea elementoutput elementprogress elementmeter elementfieldset elementlegend elementname attributedirname attributemaxlength attributeminlength attributedisabled attributedetails elementsummary elementa element to define a commandbutton element to define a commandinput element to define a commandoption element to define a commandaccesskey attribute
on a legend element to define a commandaccesskey
attribute to define a command on other elementsdialog elementscript elementnoscript elementtemplate elementslot elementcanvas elementPath2D objectsImageBitmap rendering contextOffscreenCanvas interfacecanvas elementshidden attributecontenteditable content attributedesignMode
IDL attributeinputmode attributeenterkeyhint
attributeWindow,
WindowProxy, and Location objectsWindow objectWindowProxy exotic objectHistory interfaceLocation interfacemultipart/x-mixed-replace resourcesWindowOrWorkerGlobalScope mixinbutton elementdetails and summary elementsinput element as a text entry widgetinput element as domain-specific widgetsinput element as a range controlinput element as a color
wellinput element as a checkbox and radio button widgetsinput element as a file upload controlinput element as a buttonmarquee elementmeter elementprogress elementselect elementtextarea elementThis specification defines a big part of the Web platform, in lots of detail. Its place in the Web platform specification stack relative to other specifications can be best summed up as follows:
This section is non-normative.
In short: Yes.
In more length: the term "HTML5" is widely used as a buzzword to refer to modern Web technologies, many of which (though by no means all) are developed at the WHATWG. This document is one such; others are available from the WHATWG specification index.
Although we have asked them to stop doing so, the W3C also republishes some parts of this specification as separate documents.
This section is non-normative.
HTML is the World Wide Web's core markup language. Originally, HTML was primarily designed as a language for semantically describing scientific documents. Its general design, however, has enabled it to be adapted, over the subsequent years, to describe a number of other types of documents and even applications.
This section is non-normative.
This specification is intended for authors of documents and scripts that use the features defined in this specification, implementers of tools that operate on pages that use the features defined in this specification, and individuals wishing to establish the correctness of documents or implementations with respect to the requirements of this specification.
This document is probably not suited to readers who do not already have at least a passing familiarity with Web technologies, as in places it sacrifices clarity for precision, and brevity for completeness. More approachable tutorials and authoring guides can provide a gentler introduction to the topic.
In particular, familiarity with the basics of DOM is necessary for a complete understanding of some of the more technical parts of this specification. An understanding of Web IDL, HTTP, XML, Unicode, character encodings, JavaScript, and CSS will also be helpful in places but is not essential.
This section is non-normative.
This specification is limited to providing a semantic-level markup language and associated semantic-level scripting APIs for authoring accessible pages on the Web ranging from static documents to dynamic applications.
The scope of this specification does not include providing mechanisms for media-specific customization of presentation (although default rendering rules for Web browsers are included at the end of this specification, and several mechanisms for hooking into CSS are provided as part of the language).
The scope of this specification is not to describe an entire operating system. In particular, hardware configuration software, image manipulation tools, and applications that users would be expected to use with high-end workstations on a daily basis are out of scope. In terms of applications, this specification is targeted specifically at applications that would be expected to be used by users on an occasional basis, or regularly but from disparate locations, with low CPU requirements. Examples of such applications include online purchasing systems, searching systems, games (especially multiplayer online games), public telephone books or address books, communications software (e-mail clients, instant messaging clients, discussion software), document editing software, etc.
This section is non-normative.
For its first five years (1990-1995), HTML went through a number of revisions and experienced a number of extensions, primarily hosted first at CERN, and then at the IETF.
With the creation of the W3C, HTML's development changed venue again. A first abortive attempt at extending HTML in 1995 known as HTML 3.0 then made way to a more pragmatic approach known as HTML 3.2, which was completed in 1997. HTML4 quickly followed later that same year.
The following year, the W3C membership decided to stop evolving HTML and instead begin work on an XML-based equivalent, called XHTML. This effort started with a reformulation of HTML4 in XML, known as XHTML 1.0, which added no new features except the new serialization, and which was completed in 2000. After XHTML 1.0, the W3C's focus turned to making it easier for other working groups to extend XHTML, under the banner of XHTML Modularization. In parallel with this, the W3C also worked on a new language that was not compatible with the earlier HTML and XHTML languages, calling it XHTML2.
Around the time that HTML's evolution was stopped in 1998, parts of the API for HTML developed by browser vendors were specified and published under the name DOM Level 1 (in 1998) and DOM Level 2 Core and DOM Level 2 HTML (starting in 2000 and culminating in 2003). These efforts then petered out, with some DOM Level 3 specifications published in 2004 but the working group being closed before all the Level 3 drafts were completed.
In 2003, the publication of XForms, a technology which was positioned as the next generation of Web forms, sparked a renewed interest in evolving HTML itself, rather than finding replacements for it. This interest was borne from the realization that XML's deployment as a Web technology was limited to entirely new technologies (like RSS and later Atom), rather than as a replacement for existing deployed technologies (like HTML).
A proof of concept to show that it was possible to extend HTML4's forms to provide many of the features that XForms 1.0 introduced, without requiring browsers to implement rendering engines that were incompatible with existing HTML Web pages, was the first result of this renewed interest. At this early stage, while the draft was already publicly available, and input was already being solicited from all sources, the specification was only under Opera Software's copyright.
The idea that HTML's evolution should be reopened was tested at a W3C workshop in 2004, where some of the principles that underlie the HTML5 work (described below), as well as the aforementioned early draft proposal covering just forms-related features, were presented to the W3C jointly by Mozilla and Opera. The proposal was rejected on the grounds that the proposal conflicted with the previously chosen direction for the Web's evolution; the W3C staff and membership voted to continue developing XML-based replacements instead.
Shortly thereafter, Apple, Mozilla, and Opera jointly announced their intent to continue working on the effort under the umbrella of a new venue called the WHATWG. A public mailing list was created, and the draft was moved to the WHATWG site. The copyright was subsequently amended to be jointly owned by all three vendors, and to allow reuse of the specification.
The WHATWG was based on several core principles, in particular that technologies need to be backwards compatible, that specifications and implementations need to match even if this means changing the specification rather than the implementations, and that specifications need to be detailed enough that implementations can achieve complete interoperability without reverse-engineering each other.
The latter requirement in particular required that the scope of the HTML5 specification include what had previously been specified in three separate documents: HTML4, XHTML1, and DOM2 HTML. It also meant including significantly more detail than had previously been considered the norm.
In 2006, the W3C indicated an interest to participate in the development of HTML5 after all, and in 2007 formed a working group chartered to work with the WHATWG on the development of the HTML5 specification. Apple, Mozilla, and Opera allowed the W3C to publish the specification under the W3C copyright, while keeping a version with the less restrictive license on the WHATWG site.
For a number of years, both groups then worked together. In 2011, however, the groups came to the conclusion that they had different goals: the W3C wanted to publish a "finished" version of "HTML5", while the WHATWG wanted to continue working on a Living Standard for HTML, continuously maintaining the specification rather than freezing it in a state with known problems, and adding new features as needed to evolve the platform.
Since then, the WHATWG has been working on this specification (amongst others), and the W3C has been copying fixes made by the WHATWG into their fork of the document (which also has other changes).
This section is non-normative.
It must be admitted that many aspects of HTML appear at first glance to be nonsensical and inconsistent.
HTML, its supporting DOM APIs, as well as many of its supporting technologies, have been developed over a period of several decades by a wide array of people with different priorities who, in many cases, did not know of each other's existence.
Features have thus arisen from many sources, and have not always been designed in especially consistent ways. Furthermore, because of the unique characteristics of the Web, implementation bugs have often become de-facto, and now de-jure, standards, as content is often unintentionally written in ways that rely on them before they can be fixed.
Despite all this, efforts have been made to adhere to certain design goals. These are described in the next few subsections.
This section is non-normative.
To avoid exposing Web authors to the complexities of multithreading, the HTML and DOM APIs are designed such that no script can ever detect the simultaneous execution of other scripts. Even with workers, the intent is that the behavior of implementations can be thought of as completely serializing the execution of all scripts in all browsing contexts.
The exception to this general design principle is the JavaScript SharedArrayBuffer
class. Using SharedArrayBuffer objects, it can in fact be observed that scripts in
other agents are executing simultaneously. Furthermore, due to the
JavaScript memory model, there are situations which not only are un-representable via serialized
script execution, but also un-representable via serialized statement execution
among those scripts.
This section is non-normative.
This specification interacts with and relies on a wide variety of other specifications. In certain circumstances, unfortunately, conflicting needs have led to this specification violating the requirements of these other specifications. Whenever this has occurred, the transgressions have each been noted as a "willful violation", and the reason for the violation has been noted.
This section is non-normative.
HTML has a wide array of extensibility mechanisms that can be used for adding semantics in a safe manner:
Authors can use the class attribute to extend elements,
effectively creating their own elements, while using the most applicable existing "real" HTML
element, so that browsers and other tools that don't know of the extension can still support it
somewhat well. This is the tack used by microformats, for example.
Authors can include data for inline client-side scripts or server-side site-wide scripts
to process using the data-*="" attributes. These are guaranteed
to never be touched by browsers, and allow scripts to include data on HTML elements that scripts
can then look for and process.
Authors can use the <meta name="" content=""> mechanism to
include page-wide metadata.
Authors can use the rel="" mechanism to annotate
links with specific meanings by registering extensions to
the predefined set of link types. This is also used by microformats.
Authors can embed raw data using the <script type="">
mechanism with a custom type, for further handling by inline or server-side scripts.
Authors can create plugins and invoke them using the
embed element. This is how Flash works.
Authors can extend APIs using the JavaScript prototyping mechanism. This is widely used by script libraries, for instance.
Authors can use the microdata feature (the itemscope="" and itemprop=""
attributes) to embed nested name-value pairs of data to be shared with other applications and
sites.
This section is non-normative.
This specification defines an abstract language for describing documents and applications, and some APIs for interacting with in-memory representations of resources that use this language.
The in-memory representation is known as "DOM HTML", or "the DOM" for short.
There are various concrete syntaxes that can be used to transmit resources that use this abstract language, two of which are defined in this specification.
The first such concrete syntax is the HTML syntax. This is the format suggested for most
authors. It is compatible with most legacy Web browsers. If a document is transmitted with the
text/html MIME type, then it will be processed as an HTML document by
Web browsers. This specification defines the latest HTML syntax, known simply as "HTML".
The second concrete syntax is XML. When a document is transmitted with an XML MIME
type, such as application/xhtml+xml, then it is treated as an XML document by
Web browsers, to be parsed by an XML processor. Authors are reminded that the processing for XML
and HTML differs; in particular, even minor syntax errors will prevent a document labeled as XML
from being rendered fully, whereas they would be ignored in the HTML syntax.
The XML syntax for HTML was formerly referred to as "XHTML", but this specification does not use that term (among other reasons, because no such term is used for the HTML syntaxes of MathML and SVG).
The DOM, the HTML syntax, and the XML syntax cannot all represent the same content. For
example, namespaces cannot be represented using the HTML syntax, but they are supported in the DOM
and in the XML syntax. Similarly, documents that use the noscript feature can be
represented using the HTML syntax, but cannot be represented with the DOM or in the XML syntax.
Comments that contain the string "-->" can only be represented in the
DOM, not in the HTML and XML syntaxes.
This section is non-normative.
This specification is divided into the following major sections:
EventSource, and a two-way full-duplex socket protocol for scripts known as Web
Sockets.
There are also some appendices, listing obsolete features and IANA considerations, and several indices.
This specification should be read like all other specifications. First, it should be read cover-to-cover, multiple times. Then, it should be read backwards at least once. Then it should be read by picking random sections from the contents list and following all the cross-references.
As described in the conformance requirements section below, this specification describes conformance criteria for a variety of conformance classes. In particular, there are conformance requirements that apply to producers, for example authors and the documents they create, and there are conformance requirements that apply to consumers, for example Web browsers. They can be distinguished by what they are requiring: a requirement on a producer states what is allowed, while a requirement on a consumer states how software is to act.
For example, "the foo attribute's value must be a valid
integer" is a requirement on producers, as it lays out the allowed values; in contrast,
the requirement "the foo attribute's value must be parsed using the
rules for parsing integers" is a requirement on consumers, as it describes how to
process the content.
Requirements on producers have no bearing whatsoever on consumers.
Continuing the above example, a requirement stating that a particular attribute's value is constrained to being a valid integer emphatically does not imply anything about the requirements on consumers. It might be that the consumers are in fact required to treat the attribute as an opaque string, completely unaffected by whether the value conforms to the requirements or not. It might be (as in the previous example) that the consumers are required to parse the value using specific rules that define how invalid (non-numeric in this case) values are to be processed.
This is a definition, requirement, or explanation.
This is a note.
This is an example.
This is an open issue.
This is a warning.
[Exposed =Window ]
interface Example {
// this is an IDL definition
};method( [ optionalArgument ] )This is a note to authors describing the usage of an interface.
/* this is a CSS fragment */ The defining instance of a term is marked up like this. Uses of that term are marked up like this or like this.
The defining instance of an element, attribute, or API is marked up like this. References to that element, attribute, or API are marked up
like this.
Other code fragments are marked up like this.
Variables are marked up like this.
In an algorithm, steps in synchronous sections are marked with ⌛.
In some cases, requirements are given in the form of lists with conditions and corresponding requirements. In such cases, the requirements that apply to a condition are always the first set of requirements that follow the condition, even in the case of there being multiple sets of conditions for those requirements. Such cases are presented as follows:
This section is non-normative.
Some features of HTML trade user convenience for a measure of user privacy.
In general, due to the Internet's architecture, a user can be distinguished from another by the user's IP address. IP addresses do not perfectly match to a user; as a user moves from device to device, or from network to network, their IP address will change; similarly, NAT routing, proxy servers, and shared computers enable packets that appear to all come from a single IP address to actually map to multiple users. Technologies such as onion routing can be used to further anonymize requests so that requests from a single user at one node on the Internet appear to come from many disparate parts of the network.
However, the IP address used for a user's requests is not the only mechanism by which a user's requests could be related to each other. Cookies, for example, are designed specifically to enable this, and are the basis of most of the Web's session features that enable you to log into a site with which you have an account.
There are other mechanisms that are more subtle. Certain characteristics of a user's system can be used to distinguish groups of users from each other; by collecting enough such information, an individual user's browser's "digital fingerprint" can be computed, which can be as good as, if not better than, an IP address in ascertaining which requests are from the same user.
Grouping requests in this manner, especially across multiple sites, can be used for both benign (and even arguably positive) purposes, as well as for malevolent purposes. An example of a reasonably benign purpose would be determining whether a particular person seems to prefer sites with dog illustrations as opposed to sites with cat illustrations (based on how often they visit the sites in question) and then automatically using the preferred illustrations on subsequent visits to participating sites. Malevolent purposes, however, could include governments combining information such as the person's home address (determined from the addresses they use when getting driving directions on one site) with their apparent political affiliations (determined by examining the forum sites that they participate in) to determine whether the person should be prevented from voting in an election.
Since the malevolent purposes can be remarkably evil, user agent implementers are encouraged to consider how to provide their users with tools to minimize leaking information that could be used to fingerprint a user.
Unfortunately, as the first paragraph in this section implies, sometimes there is great benefit to be derived from exposing the very information that can also be used for fingerprinting purposes, so it's not as easy as simply blocking all possible leaks. For instance, the ability to log into a site to post under a specific identity requires that the user's requests be identifiable as all being from the same user, more or less by definition. More subtly, though, information such as how wide text is, which is necessary for many effects that involve drawing text onto a canvas (e.g. any effect that involves drawing a border around the text) also leaks information that can be used to group a user's requests. (In this case, by potentially exposing, via a brute force search, which fonts a user has installed, information which can vary considerably from user to user.)
Features in this specification which can be used to
fingerprint the user are marked as this paragraph is.
Other features in the platform can be used for the same purpose, though, including, though not limited to:
Screen
object. [MQ] [CSSOMVIEW]The postMessage() API provides a mechanism by
which two sites can communicate directly. At first glance, this might appear to open a new way by
which the problems described above can occur. However, in practice, multiple mechanisms exist by
which two sites can communicate that predate this API: a site embedding another can send data via
an iframe element's dimensions; a site can use a cross-site image request with a
unique identifier known to the server to initiate a server-side data exchange; or indeed the
fingerprinting techniques described above can be used by two sites to uniquely identify a visitor
such that information can then be exchanged on the server side.
Fundamentally, users that do not trust a site to treat their information with respect have to avoid visiting that site at all.
This section is non-normative.
A basic HTML document looks like this:
<!DOCTYPE html>
< html lang = "en" >
< head >
< title > Sample page</ title >
</ head >
< body >
< h1 > Sample page</ h1 >
< p > This is a < a href = "demo.html" > simple</ a > sample.</ p >
<!-- this is a comment -->
</ body >
</ html > HTML documents consist of a tree of elements and text. Each element is denoted in the source by
a start tag, such as "<body>", and
an end tag, such as "</body>".
(Certain start tags and end tags can in certain cases be omitted and are implied by other tags.)
Tags have to be nested such that elements are all completely within each other, without overlapping:
< p > This is < em > very < strong > wrong</ em > !</ strong ></ p > < p > This < em > is < strong > correct</ strong > .</ em ></ p > This specification defines a set of elements that can be used in HTML, along with rules about the ways in which the elements can be nested.
Elements can have attributes, which control how the elements work. In the example below, there
is a hyperlink, formed using the a element and its href attribute:
< a href = "demo.html" > simple</ a > Attributes are placed inside the start tag, and consist
of a name and a value, separated by an "=" character.
The attribute value can remain unquoted if it doesn't contain ASCII
whitespace or any of " ' ` = < or >. Otherwise, it has to be quoted using either single or double quotes. The
value, along with the "=" character, can be omitted altogether if the value
is the empty string.
<!-- empty attributes -->
< input name = address disabled >
< input name = address disabled = "" >
<!-- attributes with a value -->
< input name = address maxlength = 200 >
< input name = address maxlength = '200' >
< input name = address maxlength = "200" > HTML user agents (e.g. Web browsers) then parse this markup, turning it into a DOM (Document Object Model) tree. A DOM tree is an in-memory representation of a document.
DOM trees contain several kinds of nodes, in particular a DocumentType node,
Element nodes, Text nodes, Comment nodes, and in some cases
ProcessingInstruction nodes.
The markup snippet at the top of this section would be turned into the following DOM tree:
The document element of this tree is the html element, which is the
element always found in that position in HTML documents. It contains two elements,
head and body, as well as a Text node between them.
There are many more Text nodes in the DOM tree than one would initially expect,
because the source contains a number of spaces (represented here by "␣") and line breaks
("⏎") that all end up as Text nodes in the DOM. However, for historical
reasons not all of the spaces and line breaks in the original markup appear in the DOM. In
particular, all the whitespace before head start tag ends up being dropped silently,
and all the whitespace after the body end tag ends up placed at the end of the
body.
The head element contains a title element, which itself contains a
Text node with the text "Sample page". Similarly, the body element
contains an h1 element, a p element, and a comment.
This DOM tree can be manipulated from scripts in the page. Scripts (typically in JavaScript)
are small programs that can be embedded using the script element or using event
handler content attributes. For example, here is a form with a script that sets the value
of the form's output element to say "Hello World":
< form name = "main" >
Result: < output name = "result" ></ output >
< script >
document. forms. main. elements. result. value = 'Hello World' ;
</ script >
</ form > Each element in the DOM tree is represented by an object, and these objects have APIs so that
they can be manipulated. For instance, a link (e.g. the a element in the tree above)
can have its "href" attribute changed in several
ways:
var a = document. links[ 0 ]; // obtain the first link in the document
a. href = 'sample.html' ; // change the destination URL of the link
a. protocol = 'https' ; // change just the scheme part of the URL
a. setAttribute( 'href' , 'https://example.com/' ); // change the content attribute directly Since DOM trees are used as the way to represent HTML documents when they are processed and presented by implementations (especially interactive implementations like Web browsers), this specification is mostly phrased in terms of DOM trees, instead of the markup described above.
HTML documents represent a media-independent description of interactive content. HTML documents might be rendered to a screen, or through a speech synthesizer, or on a braille display. To influence exactly how such rendering takes place, authors can use a styling language such as CSS.
In the following example, the page has been made yellow-on-blue using CSS.
<!DOCTYPE html>
< html lang = "en" >
< head >
< title > Sample styled page</ title >
< style >
body { background : navy ; color : yellow ; }
</ style >
</ head >
< body >
< h1 > Sample styled page</ h1 >
< p > This page is just a demo.</ p >
</ body >
</ html > For more details on how to use HTML, authors are encouraged to consult tutorials and guides. Some of the examples included in this specification might also be of use, but the novice author is cautioned that this specification, by necessity, defines the language with a level of detail that might be difficult to understand at first.
This section is non-normative.
When HTML is used to create interactive sites, care needs to be taken to avoid introducing vulnerabilities through which attackers can compromise the integrity of the site itself or of the site's users.
A comprehensive study of this matter is beyond the scope of this document, and authors are strongly encouraged to study the matter in more detail. However, this section attempts to provide a quick introduction to some common pitfalls in HTML application development.
The security model of the Web is based on the concept of "origins", and correspondingly many of the potential attacks on the Web involve cross-origin actions. [ORIGIN]
When accepting untrusted input, e.g. user-generated content such as text comments, values in URL parameters, messages from third-party sites, etc, it is imperative that the data be validated before use, and properly escaped when displayed. Failing to do this can allow a hostile user to perform a variety of attacks, ranging from the potentially benign, such as providing bogus user information like a negative age, to the serious, such as running scripts every time a user looks at a page that includes the information, potentially propagating the attack in the process, to the catastrophic, such as deleting all data in the server.
When writing filters to validate user input, it is imperative that filters always be safelist-based, allowing known-safe constructs and disallowing all other input. Blocklist-based filters that disallow known-bad inputs and allow everything else are not secure, as not everything that is bad is yet known (for example, because it might be invented in the future).
For example, suppose a page looked at its URL's query string to determine what to display, and the site then redirected the user to that page to display a message, as in:
< ul >
< li >< a href = "message.cgi?say=Hello" > Say Hello</ a >
< li >< a href = "message.cgi?say=Welcome" > Say Welcome</ a >
< li >< a href = "message.cgi?say=Kittens" > Say Kittens</ a >
</ ul > If the message was just displayed to the user without escaping, a hostile attacker could then craft a URL that contained a script element:
https://example.com/message.cgi?say=%3Cscript%3Ealert%28%27Oh%20no%21%27%29%3C/script%3E
If the attacker then convinced a victim user to visit this page, a script of the attacker's choosing would run on the page. Such a script could do any number of hostile actions, limited only by what the site offers: if the site is an e-commerce shop, for instance, such a script could cause the user to unknowingly make arbitrarily many unwanted purchases.
This is called a cross-site scripting attack.
There are many constructs that can be used to try to trick a site into executing code. Here are some that authors are encouraged to consider when writing safelist filters:
img, it is important to safelist
any provided attributes as well. If one allowed all attributes then an attacker could, for
instance, use the onload attribute to run arbitrary
script.javascript:", but user agents can
implement (and indeed, have historically implemented) others.base element to be inserted means any script elements
in the page with relative links can be hijacked, and similarly that any form submissions can
get redirected to a hostile site.If a site allows a user to make form submissions with user-specific side-effects, for example posting messages on a forum under the user's name, making purchases, or applying for a passport, it is important to verify that the request was made by the user intentionally, rather than by another site tricking the user into making the request unknowingly.
This problem exists because HTML forms can be submitted to other origins.
Sites can prevent such attacks by populating forms with user-specific hidden tokens, or by
checking `Origin` headers on all requests.
A page that provides users with an interface to perform actions that the user might not wish to perform needs to be designed so as to avoid the possibility that users can be tricked into activating the interface.
One way that a user could be so tricked is if a hostile site places the victim site in a
small iframe and then convinces the user to click, for instance by having the user
play a reaction game. Once the user is playing the game, the hostile site can quickly position
the iframe under the mouse cursor just as the user is about to click, thus tricking the user
into clicking the victim site's interface.
To avoid this, sites that do not expect to be used in frames are encouraged to only enable
their interface if they detect that they are not in a frame (e.g. by comparing the window object to the value of the top
attribute).
This section is non-normative.
Scripts in HTML have "run-to-completion" semantics, meaning that the browser will generally run the script uninterrupted before doing anything else, such as firing further events or continuing to parse the document.
On the other hand, parsing of HTML files happens incrementally, meaning that the parser can pause at any point to let scripts run. This is generally a good thing, but it does mean that authors need to be careful to avoid hooking event handlers after the events could have possibly fired.
There are two techniques for doing this reliably: use event handler content attributes, or create the element and add the event handlers in the same script. The latter is safe because, as mentioned earlier, scripts are run to completion before further events can fire.
One way this could manifest itself is with img elements and the load event. The event could fire as soon as the element has been
parsed, especially if the image has already been cached (which is common).
Here, the author uses the onload handler on an
img element to catch the load event:
< img src = "games.png" alt = "Games" onload = "gamesLogoHasLoaded(event)" > If the element is being added by script, then so long as the event handlers are added in the same script, the event will still not be missed:
< script >
var img = new Image();
img. src = 'games.png' ;
img. alt = 'Games' ;
img. onload = gamesLogoHasLoaded;
// img.addEventListener('load', gamesLogoHasLoaded, false); // would work also
</ script > However, if the author first created the img element and then in a separate
script added the event listeners, there's a chance that the load
event would be fired in between, leading it to be missed:
<!-- Do not use this style, it has a race condition! -->
< img id = "games" src = "games.png" alt = "Games" >
<!-- the 'load' event might fire here while the parser is taking a
break, in which case you will not see it! -->
< script >
var img = document. getElementById( 'games' );
img. onload = gamesLogoHasLoaded; // might never fire!
</ script > This section is non-normative.
Authors are encouraged to make use of conformance checkers (also known as validators) to catch common mistakes. The WHATWG maintains a list of such tools at: https://whatwg.org/validator/
This section is non-normative.
Unlike previous versions of the HTML specification, this specification defines in some detail the required processing for invalid documents as well as valid documents.
However, even though the processing of invalid content is in most cases well-defined, conformance requirements for documents are still important: in practice, interoperability (the situation in which all implementations process particular content in a reliable and identical or equivalent way) is not the only goal of document conformance requirements. This section details some of the more common reasons for still distinguishing between a conforming document and one with errors.
This section is non-normative.
The majority of presentational features from previous versions of HTML are no longer allowed. Presentational markup in general has been found to have a number of problems:
While it is possible to use presentational markup in a way that provides users of assistive technologies (ATs) with an acceptable experience (e.g. using ARIA), doing so is significantly more difficult than doing so when using semantically-appropriate markup. Furthermore, even using such techniques doesn't help make pages accessible for non-AT non-graphical users, such as users of text-mode browsers.
Using media-independent markup, on the other hand, provides an easy way for documents to be authored in such a way that they work for more users (e.g. users of text browsers).
It is significantly easier to maintain a site written in such a way that the markup is
style-independent. For example, changing the color of a site that uses <font color=""> throughout requires changes across the entire site,
whereas a similar change to a site based on CSS can be done by changing a single file.
Presentational markup tends to be much more redundant, and thus results in larger document sizes.
For those reasons, presentational markup has been removed from HTML in this version. This change should not come as a surprise; HTML4 deprecated presentational markup many years ago and provided a mode (HTML4 Transitional) to help authors move away from presentational markup; later, XHTML 1.1 went further and obsoleted those features altogether.
The only remaining presentational markup features in HTML are the style attribute and the style element. Use of the style attribute is somewhat discouraged in production environments, but
it can be useful for rapid prototyping (where its rules can be directly moved into a separate
style sheet later) and for providing specific styles in unusual cases where a separate style sheet
would be inconvenient. Similarly, the style element can be useful in syndication or
for page-specific styles, but in general an external style sheet is likely to be more convenient
when the styles apply to multiple pages.
It is also worth noting that some elements that were previously presentational have been
redefined in this specification to be media-independent: b, i,
hr, s, small, and u.
This section is non-normative.
The syntax of HTML is constrained to avoid a wide variety of problems.
Certain invalid syntax constructs, when parsed, result in DOM trees that are highly unintuitive.
To allow user agents to be used in controlled environments without having to implement the more bizarre and convoluted error handling rules, user agents are permitted to fail whenever encountering a parse error.
Some error-handling behavior, such as the behavior for the <table><hr>... example mentioned above, are incompatible with streaming
user agents (user agents that process HTML files in one pass, without storing state). To avoid
interoperability problems with such user agents, any syntax resulting in such behavior is
considered invalid.
When a user agent based on XML is connected to an HTML parser, it is possible that certain invariants that XML enforces, such as element or attribute names never contain multiple colons, will be violated by an HTML file. Handling this can require that the parser coerce the HTML DOM into an XML-compatible infoset. Most syntax constructs that require such handling are considered invalid. (Comments containing two consecutive hyphens, or ending with a hyphen, are exceptions that are allowed in the HTML syntax.)
Certain syntax constructs can result in disproportionately poor performance. To discourage the use of such constructs, they are typically made non-conforming.
For example, the following markup results in poor performance, since all the unclosed
i elements have to be reconstructed in each paragraph, resulting in progressively
more elements in each paragraph:
< p >< i > She dreamt.
< p >< i > She dreamt that she ate breakfast.
< p >< i > Then lunch.
< p >< i > And finally dinner.The resulting DOM for this fragment would be:
There are syntax constructs that, for historical reasons, are relatively fragile. To help reduce the number of users who accidentally run into such problems, they are made non-conforming.
For example, the parsing of certain named character references in attributes happens even with the closing semicolon being omitted. It is safe to include an ampersand followed by letters that do not form a named character reference, but if the letters are changed to a string that does form a named character reference, they will be interpreted as that character instead.
In this fragment, the attribute's value is "?bill&ted":
< a href = "?bill&ted" > Bill and Ted</ a > In the following fragment, however, the attribute's value is actually "?art©", not the intended "?art©",
because even without the final semicolon, "©" is handled the same
as "©" and thus gets interpreted as "©":
< a href = "?art©" > Art and Copy</ a > To avoid this problem, all named character references are required to end with a semicolon, and uses of named character references without a semicolon are flagged as errors.
Thus, the correct way to express the above cases is as follows:
< a href = "?bill&ted" > Bill and Ted</ a > <!-- &ted is ok, since it's not a named character reference --> < a href = "?art&copy" > Art and Copy</ a > <!-- the & has to be escaped, since © is a named character reference --> Certain syntax constructs are known to cause especially subtle or serious problems in legacy user agents, and are therefore marked as non-conforming to help authors avoid them.
For example, this is why the U+0060 GRAVE ACCENT character (`) is not allowed in unquoted attributes. In certain legacy user agents, it is sometimes treated as a quote character.
Another example of this is the DOCTYPE, which is required to trigger no-quirks mode, because the behavior of legacy user agents in quirks mode is often largely undocumented.
Certain restrictions exist purely to avoid known security problems.
For example, the restriction on using UTF-7 exists purely to avoid authors falling prey to a known cross-site-scripting attack using UTF-7. [UTF7]
Markup where the author's intent is very unclear is often made non-conforming. Correcting these errors early makes later maintenance easier.
When a user makes a simple typo, it is helpful if the error can be caught early, as this can save the author a lot of debugging time. This specification therefore usually considers it an error to use element names, attribute names, and so forth, that do not match the names defined in this specification.
For example, if the author typed <capton> instead of <caption>, this would be flagged as an error and the author could correct
the typo immediately.
In order to allow the language syntax to be extended in the future, certain otherwise harmless features are disallowed.
For example, "attributes" in end tags are ignored currently, but they are invalid, in case a future change to the language makes use of that syntax feature without conflicting with already-deployed (and valid!) content.
Some authors find it helpful to be in the practice of always quoting all attributes and always including all optional tags, preferring the consistency derived from such custom over the minor benefits of terseness afforded by making use of the flexibility of the HTML syntax. To aid such authors, conformance checkers can provide modes of operation wherein such conventions are enforced.
This section is non-normative.
Beyond the syntax of the language, this specification also places restrictions on how elements and attributes can be specified. These restrictions are present for similar reasons:
To avoid misuse of elements with defined meanings, content models are defined that restrict how elements can be nested when such nestings would be of dubious value.
For example, this specification disallows nesting a section
element inside a kbd element, since it is highly unlikely for an author to indicate
that an entire section should be keyed in.
Similarly, to draw the author's attention to mistakes in the use of elements, clear contradictions in the semantics expressed are also considered conformance errors.
In the fragments below, for example, the semantics are nonsensical: a separator cannot simultaneously be a cell, nor can a radio button be a progress bar.
< hr role = "cell" > < input type = radio role = progressbar > Another example is the restrictions on the content models of the
ul element, which only allows li element children. Lists by definition
consist just of zero or more list items, so if a ul element contains something
other than an li element, it's not clear what was meant.
Certain elements have default styles or behaviors that make certain combinations likely to lead to confusion. Where these have equivalent alternatives without this problem, the confusing combinations are disallowed.
For example, div elements are rendered as block boxes, and span elements as inline boxes. Putting a block box in an
inline box is unnecessarily confusing; since either nesting just div
elements, or nesting just span elements, or nesting span elements
inside div elements all serve the same purpose as nesting a div
element in a span element, but only the latter involves a block box in
an inline box, the latter combination is disallowed.
Another example would be the way interactive content cannot be
nested. For example, a button element cannot contain a textarea
element. This is because the default behavior of such nesting interactive elements would be
highly confusing to users. Instead of nesting these elements, they can be placed side by
side.
Sometimes, something is disallowed because allowing it would likely cause author confusion.
For example, setting the disabled
attribute to the value "false" is disallowed, because despite the
appearance of meaning that the element is enabled, it in fact means that the element is
disabled (what matters for implementations is the presence of the attribute, not its
value).
Some conformance errors simplify the language that authors need to learn.
For example, the area element's shape attribute, despite accepting both circ and circle values in practice as synonyms, disallows
the use of the circ value, so as to simplify
tutorials and other learning aids. There would be no benefit to allowing both, but it would
cause extra confusion when teaching the language.
Certain elements are parsed in somewhat eccentric ways (typically for historical reasons), and their content model restrictions are intended to avoid exposing the author to these issues.
For example, a form element isn't allowed inside phrasing content,
because when parsed as HTML, a form element's start tag will imply a
p element's end tag. Thus, the following markup results in two paragraphs, not one:
< p > Welcome. < form >< label > Name:</ label > < input ></ form > It is parsed exactly like the following:
< p > Welcome. </ p >< form >< label > Name:</ label > < input ></ form > Some errors are intended to help prevent script problems that would be hard to debug.
This is why, for instance, it is non-conforming to have two id attributes with the same value. Duplicate IDs lead to the wrong
element being selected, with sometimes disastrous effects whose cause is hard to determine.
Some constructs are disallowed because historically they have been the cause of a lot of wasted authoring time, and by encouraging authors to avoid making them, authors can save time in future efforts.
For example, a script element's src attribute causes the element's contents to be ignored.
However, this isn't obvious, especially if the element's contents appear to be executable script
— which can lead to authors spending a lot of time trying to debug the inline script
without realizing that it is not executing. To reduce this problem, this specification makes it
non-conforming to have executable script in a script element when the src attribute is present. This means that authors who are
validating their documents are less likely to waste time with this kind of mistake.
Some authors like to write files that can be interpreted as both XML and HTML with similar results. Though this practice is discouraged in general due to the myriad of subtle complications involved (especially when involving scripting, styling, or any kind of automated serialization), this specification has a few restrictions intended to at least somewhat mitigate the difficulties. This makes it easier for authors to use this as a transitionary step when migrating between the HTML and XML syntaxes.
For example, there are somewhat complicated rules surrounding the lang and xml:lang attributes
intended to keep the two synchronized.
Another example would be the restrictions on the values of xmlns attributes in the HTML serialization, which are intended to ensure that
elements in conforming documents end up in the same namespaces whether processed as HTML or
XML.
As with the restrictions on the syntax intended to allow for new syntax in future revisions of the language, some restrictions on the content models of elements and values of attributes are intended to allow for future expansion of the HTML vocabulary.
For example, limiting the values of the target attribute that start with an U+005F LOW LINE
character (_) to only specific predefined values allows new predefined values to be introduced
at a future time without conflicting with author-defined values.
Certain restrictions are intended to support the restrictions made by other specifications.
For example, requiring that attributes that take media query lists use only valid media query lists reinforces the importance of following the conformance rules of that specification.
This section is non-normative.
The following documents might be of interest to readers of this specification.
This Architectural Specification provides authors of specifications, software developers, and content developers with a common reference for interoperable text manipulation on the World Wide Web, building on the Universal Character Set, defined jointly by the Unicode Standard and ISO/IEC 10646. Topics addressed include use of the terms 'character', 'encoding' and 'string', a reference processing model, choice and identification of character encodings, character escaping, and string indexing.
Because Unicode contains such a large number of characters and incorporates the varied writing systems of the world, incorrect usage can expose programs or systems to possible security attacks. This is especially important as more and more products are internationalized. This document describes some of the security considerations that programmers, system analysts, standards developers, and users should take into account, and provides specific recommendations to reduce the risk of problems.
Web Content Accessibility Guidelines (WCAG) 2.0 covers a wide range of recommendations for making Web content more accessible. Following these guidelines will make content accessible to a wider range of people with disabilities, including blindness and low vision, deafness and hearing loss, learning disabilities, cognitive limitations, limited movement, speech disabilities, photosensitivity and combinations of these. Following these guidelines will also often make your Web content more usable to users in general.
This specification provides guidelines for designing Web content authoring tools that are more accessible for people with disabilities. An authoring tool that conforms to these guidelines will promote accessibility by providing an accessible user interface to authors with disabilities as well as by enabling, supporting, and promoting the production of accessible Web content by all authors.
This document provides guidelines for designing user agents that lower barriers to Web accessibility for people with disabilities. User agents include browsers and other types of software that retrieve and render Web content. A user agent that conforms to these guidelines will promote accessibility through its own user interface and through other internal facilities, including its ability to communicate with other technologies (especially assistive technologies). Furthermore, all users, not just users with disabilities, should find conforming user agents to be more usable.
This specification depends on Infra. [INFRA]
This specification refers to both HTML and XML attributes and IDL attributes, often in the same context. When it is not clear which is being referred to, they are referred to as content attributes for HTML and XML attributes, and IDL attributes for those defined on IDL interfaces. Similarly, the term "properties" is used for both JavaScript object properties and CSS properties. When these are ambiguous they are qualified as object properties and CSS properties respectively.
Generally, when the specification states that a feature applies to the HTML syntax or the XML syntax, it also includes the other. When a feature specifically only applies to one of the two languages, it is called out by explicitly stating that it does not apply to the other format, as in "for HTML, ... (this does not apply to XML)".
This specification uses the term document to refer to any use of HTML,
ranging from short static documents to long essays or reports with rich multimedia, as well as to
fully-fledged interactive applications. The term is used to refer both to Document
objects and their descendant DOM trees, and to serialized byte streams using the HTML syntax or the XML syntax, depending
on context.
In the context of the DOM structures, the terms HTML
document and XML document are used as defined in
DOM, and refer specifically to two different modes that Document objects
can find themselves in. [DOM] (Such uses are always hyperlinked to their
definition.)
In the context of byte streams, the term HTML document refers to resources labeled as
text/html, and the term XML document refers to resources labeled with an XML
MIME type.
For simplicity, terms such as shown, displayed, and visible might sometimes be used when referring to the way a document is rendered to the user. These terms are not meant to imply a visual medium; they must be considered to apply to other media in equivalent ways.
To run steps in parallel means those steps are to be run, one after another, at the same time as other logic in the standard (e.g., at the same time as the event loop). This standard does not define the precise mechanism by which this is achieved, be it time-sharing cooperative multitasking, fibers, threads, processes, using different hyperthreads, cores, CPUs, machines, etc. By contrast, an operation that is to run immediately must interrupt the currently running task, run itself, and then resume the previously running task.
For guidance on writing specifications that leverage parallelism, see Dealing with the event loop from other specifications.
To avoid race conditions between different in parallel algorithms that operate on the same data, a parallel queue can be used.
A parallel queue represents a queue of algorithm steps that must be run in series.
A parallel queue has an algorithm queue (a queue), initially empty.
To enqueue steps to a parallel queue, enqueue the algorithm steps to the parallel queue's algorithm queue.
To start a new parallel queue, run the following steps:
Let parallelQueue be a new parallel queue.
Run the following steps in parallel:
While true:
Let steps be the result of dequeueing from parallelQueue's algorithm queue.
If steps is not nothing, then run steps.
Assert: running steps did not throw an exception, as steps running in parallel are not allowed to throw.
Implementations are not expected to implement this as a continuously running loop. Algorithms in standards are to be easy to understand and are not necessarily great for battery life or performance.
Return parallelQueue.
Steps running in parallel can themselves run other steps in in parallel. E.g., inside a parallel queue it can be useful to run a series of steps in parallel with the queue.
Imagine a standard defined nameList (a list), along with a method to add a name to nameList, unless nameList already contains name, in which case it rejects.
The following solution suffers from race conditions:
Let p be a new promise.
Run the following steps in parallel:
Return p.
Two invocations of the above could run simultaneously, meaning name isn't in nameList during step 2.1, but it might be added before step 2.3 runs, meaning name ends up in nameList twice.
Parallel queues solve this. The standard would let nameListQueue be the result of starting a new parallel queue, then:
Let p be a new promise.
Enqueue the following steps to nameListQueue:
Return p.
The steps would now queue and the race is avoided.
The specification uses the term supported when referring to whether a user agent has an implementation capable of decoding the semantics of an external resource. A format or type is said to be supported if the implementation can process an external resource of that format or type without critical aspects of the resource being ignored. Whether a specific resource is supported can depend on what features of the resource's format are in use.
For example, a PNG image would be considered to be in a supported format if its pixel data could be decoded and rendered, even if, unbeknownst to the implementation, the image also contained animation data.
An MPEG-4 video file would not be considered to be in a supported format if the compression format used was not supported, even if the implementation could determine the dimensions of the movie from the file's metadata.
What some specifications, in particular the HTTP specifications, refer to as a representation is referred to in this specification as a resource. [HTTP]
A resource's critical subresources are those that the resource needs to have available to be correctly processed. Which resources are considered critical or not is defined by the specification that defines the resource's format.
For CSS style sheets, we tentatively define here that
their critical subresources are other style sheets imported via @import
rules, including those indirectly imported by other imported style sheets.
This definition is not fully interoperable; furthermore, some user agents seem to count resources like background images or web fonts as critical subresources. Ideally, the CSS Working Group would define this; see w3c/csswg-drafts issue #1088 to track progress on that front.
To ease migration from HTML to XML, UAs conforming to this specification
will place elements in HTML in the http://www.w3.org/1999/xhtml namespace, at least for the purposes of the DOM and
CSS. The term "HTML elements" refers to any element in that namespace,
even in XML documents.
Except where otherwise stated, all elements defined or mentioned in this specification are in
the HTML namespace ("http://www.w3.org/1999/xhtml"), and all
attributes defined or mentioned in this specification have no namespace.
The term element type is used to refer to the set of elements that have a given
local name and namespace. For example, button elements are elements with the element
type button, meaning they have the local name "button" and
(implicitly as defined above) the HTML namespace.
Attribute names are said to be XML-compatible if they match the Name production defined in XML and they contain no U+003A COLON
characters (:). [XML]
When it is stated that some element or attribute is ignored, or treated as some other value, or handled as if it was something else, this refers only to the processing of the node after it is in the DOM. A user agent must not mutate the DOM in such situations.
A content attribute is said to change value only if its new value is different than its previous value; setting an attribute to a value it already has does not change it.
The term empty, when used for an attribute value, Text node,
or string, means that the length of the text is zero (i.e., not even containing controls or U+0020 SPACE).
A node A is inserted into a node B when the insertion steps are invoked with A as the argument and A's new parent is B. Similarly, a node A is removed from a node B when the removing steps are invoked with A as the removedNode argument and B as the oldParent argument.
A node is inserted into a document when the insertion steps are invoked with it as the argument and it is now in a document tree. Analogously, a node is removed from a document when the removing steps are invoked with it as the argument and it is now no longer in a document tree.
A node becomes connected when the insertion steps are invoked with it as the argument and it is now connected. Analogously, a node becomes disconnected when the removing steps are invoked with it as the argument and it is now no longer connected.
A node is browsing-context connected when it is connected and its shadow-including root's browsing context is non-null. A node becomes browsing-context connected when the insertion steps are invoked with it as the argument and it is now browsing-context connected. A node becomes browsing-context disconnected either when the removing steps are invoked with it as the argument and it is now no longer browsing-context connected, or when its shadow-including root's browsing context becomes null.
The construction "a Foo object", where Foo is
actually an interface, is sometimes used instead of the more accurate "an object implementing the
interface Foo".
An IDL attribute is said to be getting when its value is being retrieved (e.g. by author script), and is said to be setting when a new value is assigned to it.
If a DOM object is said to be live, then the attributes and methods on that object must operate on the actual underlying data, not a snapshot of the data.
The term plugin refers to a user-agent defined set of content handlers used by the
user agent that can take part in the user agent's rendering of a Document object, but
that neither act as child browsing contexts of the
Document nor introduce any Node objects to the Document's
DOM.
Typically such content handlers are provided by third parties, though a user agent can also designate built-in content handlers as plugins.
A user agent must not consider the types text/plain and
application/octet-stream as having a registered plugin.
One example of a plugin would be a PDF viewer that is instantiated in a browsing context when the user navigates to a PDF file. This would count as a plugin regardless of whether the party that implemented the PDF viewer component was the same as that which implemented the user agent itself. However, a PDF viewer application that launches separate from the user agent (as opposed to using the same interface) is not a plugin by this definition.
This specification does not define a mechanism for interacting with plugins, as it is expected to be user-agent- and platform-specific. Some UAs might opt to support a plugin mechanism such as the Netscape Plugin API; others might use remote content converters or have built-in support for certain types. Indeed, this specification doesn't require user agents to support plugins at all. [NPAPI]
A plugin can be secured if it honors the semantics of
the sandbox attribute.
For example, a secured plugin would prevent its contents from creating pop-up
windows when the plugin is instantiated inside a sandboxed iframe.
Browsers should take extreme care when interacting with external content intended for plugins. When third-party software is run with the same privileges as the user agent itself, vulnerabilities in the third-party software become as dangerous as those in the user agent.
Since different users having different sets of plugins provides a
fingerprinting vector that increases the chances of users being uniquely identified, user agents
are encouraged to support the exact same set of plugins for each
user.
A character encoding, or just encoding where that is not ambiguous, is a defined way to convert between byte streams and Unicode strings, as defined in Encoding. An encoding has an encoding name and one or more encoding labels, referred to as the encoding's name and labels in the Encoding standard. [ENCODING]
A UTF-16 encoding is UTF-16BE or UTF-16LE. [ENCODING]
An ASCII-compatible encoding is any encoding that is not a UTF-16 encoding. [ENCODING]
Since support for encodings that are not defined in Encoding is prohibited, UTF-16 encodings are the only encodings that this specification needs to treat as not being ASCII-compatible encodings.
This specification describes the conformance criteria for user agents (relevant to implementers) and documents (relevant to authors and authoring tool implementers).
Conforming documents are those that comply with all the conformance criteria for documents. For readability, some of these conformance requirements are phrased as conformance requirements on authors; such requirements are implicitly requirements on documents: by definition, all documents are assumed to have had an author. (In some cases, that author may itself be a user agent — such user agents are subject to additional rules, as explained below.)
For example, if a requirement states that "authors must not
use the foobar element", it would imply that documents are not allowed to
contain elements named foobar.
There is no implied relationship between document conformance requirements and implementation conformance requirements. User agents are not free to handle non-conformant documents as they please; the processing model described in this specification applies to implementations regardless of the conformity of the input documents.
User agents fall into several (overlapping) categories with different conformance requirements.
Web browsers that support the XML syntax must process elements and attributes from the HTML namespace found in XML documents as described in this specification, so that users can interact with them, unless the semantics of those elements have been overridden by other specifications.
A conforming Web browser would, upon finding a script element in
an XML document, execute the script contained in that element. However, if the element is found
within a transformation expressed in XSLT (assuming the user agent also supports XSLT), then the
processor would instead treat the script element as an opaque element that forms
part of the transform.
Web browsers that support the HTML syntax must process documents labeled with an HTML MIME type as described in this specification, so that users can interact with them.
User agents that support scripting must also be conforming implementations of the IDL fragments in this specification, as described in Web IDL. [WEBIDL]
Unless explicitly stated, specifications that override the semantics of HTML
elements do not override the requirements on DOM objects representing those elements. For
example, the script element in the example above would still implement the
HTMLScriptElement interface.
User agents that process HTML and XML documents purely to render non-interactive versions of them must comply to the same conformance criteria as Web browsers, except that they are exempt from requirements regarding user interaction.
Typical examples of non-interactive presentation user agents are printers (static UAs) and overhead displays (dynamic UAs). It is expected that most static non-interactive presentation user agents will also opt to lack scripting support.
A non-interactive but dynamic presentation UA would still execute scripts, allowing forms to be dynamically submitted, and so forth. However, since the concept of "focus" is irrelevant when the user cannot interact with the document, the UA would not need to support any of the focus-related DOM APIs.
User agents, whether interactive or not, may be designated (possibly as a user option) as supporting the suggested default rendering defined by this specification.
This is not required. In particular, even user agents that do implement the suggested default rendering are encouraged to offer settings that override this default to improve the experience for the user, e.g. changing the color contrast, using different focus styles, or otherwise making the experience more accessible and usable to the user.
User agents that are designated as supporting the suggested default rendering must, while so designated, implement the rules the rendering section defines as the behavior that user agents are expected to implement.
Implementations that do not support scripting (or which have their scripting features disabled entirely) are exempt from supporting the events and DOM interfaces mentioned in this specification. For the parts of this specification that are defined in terms of an events model or in terms of the DOM, such user agents must still act as if events and the DOM were supported.
Scripting can form an integral part of an application. Web browsers that do not support scripting, or that have scripting disabled, might be unable to fully convey the author's intent.
Conformance checkers must verify that a document conforms to the applicable conformance
criteria described in this specification. Automated conformance checkers are exempt from
detecting errors that require interpretation of the author's intent (for example, while a
document is non-conforming if the content of a blockquote element is not a quote,
conformance checkers running without the input of human judgement do not have to check that
blockquote elements only contain quoted material).
Conformance checkers must check that the input document conforms when parsed without a browsing context (meaning that no scripts are run, and that the parser's scripting flag is disabled), and should also check that the input document conforms when parsed with a browsing context in which scripts execute, and that the scripts never cause non-conforming states to occur other than transiently during script execution itself. (This is only a "SHOULD" and not a "MUST" requirement because it has been proven to be impossible. [COMPUTABLE])
The term "HTML validator" can be used to refer to a conformance checker that itself conforms to the applicable requirements of this specification.
XML DTDs cannot express all the conformance requirements of this specification. Therefore, a validating XML processor and a DTD cannot constitute a conformance checker. Also, since neither of the two authoring formats defined in this specification are applications of SGML, a validating SGML system cannot constitute a conformance checker either.
To put it another way, there are three types of conformance criteria:
A conformance checker must check for the first two. A simple DTD-based validator only checks for the first class of errors and is therefore not a conforming conformance checker according to this specification.
Applications and tools that process HTML and XML documents for reasons other than to either render the documents or check them for conformance should act in accordance with the semantics of the documents that they process.
A tool that generates document outlines but increases the nesting level for each paragraph and does not increase the nesting level for each section would not be conforming.
Authoring tools and markup generators must generate conforming documents. Conformance criteria that apply to authors also apply to authoring tools, where appropriate.
Authoring tools are exempt from the strict requirements of using elements only for their specified purpose, but only to the extent that authoring tools are not yet able to determine author intent. However, authoring tools must not automatically misuse elements or encourage their users to do so.
For example, it is not conforming to use an address element for
arbitrary contact information; that element can only be used for marking up contact information
for its nearest article or body element ancestor. However, since an
authoring tool is likely unable to determine the difference, an authoring tool is exempt from
that requirement. This does not mean, though, that authoring tools can use address
elements for any block of italics text (for instance); it just means that the authoring tool
doesn't have to verify that when the user uses a tool for inserting contact information for an
article element, that the user really is doing that and not inserting something
else instead.
In terms of conformance checking, an editor has to output documents that conform to the same extent that a conformance checker will verify.
When an authoring tool is used to edit a non-conforming document, it may preserve the conformance errors in sections of the document that were not edited during the editing session (i.e. an editing tool is allowed to round-trip erroneous content). However, an authoring tool must not claim that the output is conformant if errors have been so preserved.
Authoring tools are expected to come in two broad varieties: tools that work from structure or semantic data, and tools that work on a What-You-See-Is-What-You-Get media-specific editing basis (WYSIWYG).
The former is the preferred mechanism for tools that author HTML, since the structure in the source information can be used to make informed choices regarding which HTML elements and attributes are most appropriate.
However, WYSIWYG tools are legitimate. WYSIWYG tools should use elements they know are
appropriate, and should not use elements that they do not know to be appropriate. This might in
certain extreme cases mean limiting the use of flow elements to just a few elements, like
div, b, i, and span and making liberal use
of the style attribute.
All authoring tools, whether WYSIWYG or not, should make a best effort attempt at enabling users to create well-structured, semantically rich, media-independent content.
User agents may impose implementation-specific limits on otherwise
unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of
memory, or to work around platform-specific limitations.
For compatibility with existing content and prior specifications, this specification describes two authoring formats: one based on XML, and one using a custom format inspired by SGML (referred to as the HTML syntax). Implementations must support at least one of these two formats, although supporting both is encouraged.
Some conformance requirements are phrased as requirements on elements, attributes, methods or objects. Such requirements fall into two categories: those describing content model restrictions, and those describing implementation behavior. Those in the former category are requirements on documents and authoring tools. Those in the second category are requirements on user agents. Similarly, some conformance requirements are phrased as requirements on authors; such requirements are to be interpreted as conformance requirements on the documents that authors produce. (In other words, this specification does not distinguish between conformance criteria on authors and conformance criteria on documents.)
This specification relies on several other underlying specifications.
The following terms are defined in Infra: [INFRA]
The Unicode character set is used to represent textual data, and Encoding defines requirements around character encodings. [UNICODE]
This specification introduces terminology based on the terms defined in those specifications, as described earlier.
The following terms are used as defined in Encoding: [ENCODING]
Implementations that support the XML syntax for HTML must support some version of XML, as well as its corresponding namespaces specification, because that syntax uses an XML serialization with namespaces. [XML] [XMLNS]
Data mining tools and other user agents that perform operations on content without running scripts, evaluating CSS or XPath expressions, or otherwise exposing the resulting DOM to arbitrary content, may "support namespaces" by just asserting that their DOM node analogues are in certain namespaces, without actually exposing the namespace strings.
In the HTML syntax, namespace prefixes and namespace declarations do not have the same effect as in XML. For instance, the colon has no special meaning in HTML element names.
The attribute with the tag name xml:space in
the XML namespace is defined by Extensible Markup Language
(XML). [XML]
The Name production is defined in XML. [XML]
This specification also references the <?xml-stylesheet?>
processing instruction, defined in Associating Style Sheets with XML documents. [XMLSSPI]
This specification also non-normatively mentions the XSLTProcessor
interface and its transformToFragment() and transformToDocument() methods. [XSLTP]
The following terms are defined in URL: [URL]
application/x-www-form-urlencoded formatapplication/x-www-form-urlencoded serializerA number of schemes and protocols are referenced by this specification also:
about: scheme [ABOUT]blob: scheme [FILEAPI]data: scheme [RFC2397]http: scheme [HTTP]https: scheme [HTTP]mailto: scheme [MAILTO]sms: scheme [SMS]urn: scheme [URN]Media fragment syntax is defined in Media Fragments URI. [MEDIAFRAG]
The following terms are defined in the HTTP specifications: [HTTP]
Accept` headerAccept-Language` headerCache-Control` headerContent-Disposition` headerContent-Language` headerLast-Modified` headerReferer` headerThe following terms are defined in HTTP State Management Mechanism: [COOKIES]
Cookie` headerThe following term is defined in Web Linking: [WEBLINK]
Link` headerThe following terms are defined in MIME Sniffing: [MIMESNIFF]
The following terms are defined in Fetch: [FETCH]
about:blankUser-Agent` valueOrigin` headerRequestCredentials enumerationRequestDestination enumerationfetch() methodThe following terms are defined in Referrer Policy: [REFERRERPOLICY]
Referrer-Policy` HTTP headerReferrer-Policy` header algorithmno-referrer",
"no-referrer-when-downgrade",
"origin-when-cross-origin", and
"unsafe-url" referrer policiesThe following terms are defined in Mixed Content: [MIX]
The following terms are defined in Paint Timing: [PAINTTIMING]
The following terms are defined in Long Tasks: [LONGTASKS]
The IDL fragments in this specification must be interpreted as required for conforming IDL fragments, as described in Web IDL. [WEBIDL]
The following terms are defined in Web IDL:
The Web IDL also defines the following types that are used in Web IDL fragments in this specification:
ArrayBufferArrayBufferViewbooleanDOMStringdoubleErrorFunctionlongobjectUint8ClampedArrayunrestricted doubleunsigned longUSVStringVoidFunctionThe term throw in this
specification is used as defined in Web IDL. The DOMException
type and the following exception names are defined by Web IDL and used by this
specification:
IndexSizeError"HierarchyRequestError"InvalidCharacterError"NotFoundError"NotSupportedError"InvalidStateError"SyntaxError"InvalidAccessError"SecurityError"NetworkError"AbortError"QuotaExceededError"DataCloneError"EncodingError"NotAllowedError"When this specification requires a user agent to create a Date object
representing a particular time (which could be the special value Not-a-Number), the milliseconds
component of that time, if any, must be truncated to an integer, and the time value of the newly
created Date object must represent the resulting truncated time.
For instance, given the time 23045 millionths of a second after 01:00 UTC on
January 1st 2000, i.e. the time 2000-01-01T00:00:00.023045Z, then the Date object
created representing that time would represent the same time as that created representing the
time 2000-01-01T00:00:00.023Z, 45 millionths earlier. If the given time is NaN, then the result
is a Date object that represents a time value NaN (indicating that the object does
not represent a specific instant of time).
Some parts of the language described by this specification only support JavaScript as the underlying scripting language. [JAVASCRIPT]
The term "JavaScript" is used to refer to ECMA-262, rather than the official
term ECMAScript, since the term JavaScript is more widely known. Similarly, the MIME
type used to refer to JavaScript in this specification is text/javascript, since that is the most commonly used type, despite it being an officially obsoleted type according to RFC
4329. [RFC4329]
The following terms are defined in the JavaScript specification and used in this specification:
Date classSharedArrayBuffer classTypeError classRangeError classeval() functionimport()typeof operatordelete operatorUser agents that support JavaScript must also implement the import.meta proposal. The following term is defined there, and used in this specification: [JSIMPORTMETA]
import.metaUsers agents that support JavaScript must also implement ECMAScript Internationalization API. [JSINTL]
User agents that support JavaScript must also implement the BigInt proposal. [JSBIGINT]
The Document Object Model (DOM) is a representation — a model — of a document and its content. The DOM is not just an API; the conformance criteria of HTML implementations are defined, in this specification, in terms of operations on the DOM. [DOM]
Implementations must support DOM and the events defined in UI Events, because this specification is defined in terms of the DOM, and some of the features are defined as extensions to the DOM interfaces. [DOM] [UIEVENTS]
In particular, the following features are defined in DOM: [DOM]
Attr interfaceComment interfaceDOMImplementation interfaceDocument interfaceDocumentOrShadowRoot interfaceDocumentFragment interfaceDocumentType interfaceChildNode interfaceElement interfaceattachShadow() method.Node interfaceNodeList interfaceProcessingInstruction interfaceShadowRoot interfaceText interfaceHTMLCollection interfaceHTMLCollection.length attributeHTMLCollection.item() methodHTMLCollection.namedItem() methodDOMTokenList interfaceDOMTokenList.value attributecreateDocument() methodcreateHTMLDocument() methodcreateElement() methodcreateElementNS() methodgetElementById() methodgetElementsByClassName() methodappendChild() methodcloneNode() methodimportNode() methodpreventDefault() methodid attributetextContent attributeEvent interfaceEventTarget interfaceEventInit dictionary typetype attributetarget attributecurrentTarget attributebubbles attributecancelable attributeisTrusted attributeinitEvent() methodaddEventListener() methodEventListener callback interfaceDocumentNode, and the concept of
cloning steps used by that algorithmis valueMutationObserver interface and mutation observers in generalThe following features are defined in UI Events: [UIEVENTS]
MouseEvent interfaceMouseEvent interface's relatedTarget attributeMouseEventInit dictionary typeFocusEvent interfaceFocusEvent interface's relatedTarget attributeUIEvent interfaceUIEvent interface's view attributeauxclick eventclick eventdblclick eventmousedown eventmouseenter eventmouseleave eventmousemove eventmouseout eventmouseover eventmouseup eventwheel eventkeydown eventkeypress eventkeyup eventThe following features are defined in Touch Events: [TOUCH]
Touch interfacetouchend eventThe following features are defined in Pointer Events: [POINTEREVENTS]
pointerup eventThis specification sometimes uses the term name to refer to the event's
type; as in, "an event named click" or "if the event name is keypress". The terms
"name" and "type" for events are synonymous.
The following features are defined in DOM Parsing and Serialization: [DOMPARSING]
The Selection
interface is defined in the Selection API specification. [SELECTION]
User agents are encouraged to implement the features described in execCommand. [EXECCOMMAND]
The following parts of Fullscreen API are referenced from this
specification, in part to define the rendering of dialog elements, and also to
define how the Fullscreen API interacts with HTML: [FULLSCREEN]
requestFullscreen()High Resolution Time provides the current high
resolution time and the DOMHighResTimeStamp
typedef. [HRT]
This specification uses the following features defined in File API: [FILEAPI]
Blob interface and its
type attributeFile interface and its
name and
lastModified attributesFileList interfaceBlob's snapshot stateThis specification uses cleanup Indexed Database transactions defined by Indexed Database API. [INDEXEDDB]
The following terms are defined in Media Source Extensions: [MEDIASOURCE]
The following terms are defined in Media Capture and Streams: [MEDIASTREAM]
MediaStream interfaceThe following features and terms are defined in XMLHttpRequest: [XHR]
XMLHttpRequest interfaceXMLHttpRequest.responseXML attributeProgressEvent interfaceProgressEvent.lengthComputable attributeProgressEvent.loaded attributeProgressEvent.total attributeFormData
interfaceFormDataEntryValue
typeThe following features are defined in Battery Status API: [BATTERY]
getBattery() methodImplementations must support Media Queries. The <media-condition> feature is defined therein. [MQ]
While support for CSS as a whole is not required of implementations of this specification (though it is encouraged, at least for Web browsers), some features are defined in terms of specific CSS requirements.
When this specification requires that something be parsed according to a particular CSS grammar, the relevant algorithm in CSS Syntax must be followed, including error handling rules. [CSSSYNTAX]
For example, user agents are required to close all open constructs upon
finding the end of a style sheet unexpectedly. Thus, when parsing the string "rgb(0,0,0" (with a missing close-parenthesis) for a color value, the close
parenthesis is implied by this error handling rule, and a value is obtained (the color 'black').
However, the similar construct "rgb(0,0," (with both a missing
parenthesis and a missing "blue" value) cannot be parsed, as closing the open construct does not
result in a viable value.
To parse a CSS <color> value, given a string input with an optional element element, run these steps:
Let color be the result of parsing input as a CSS <color>. [CSSCOLOR]
If color is failure, then return failure.
If color is 'currentcolor', then:
If element is not given, then set color to opaque black.
Otherwise, set color to the computed value of the 'color' property of element.
Return color.
The following terms and features are defined in Cascading Style Sheets (CSS): [CSS]
CSS also defines the following border properties: [CSS]
| Top | Bottom | Left | Right | |
|---|---|---|---|---|
| Width | 'border-top-width' | 'border-bottom-width' | 'border-left-width' | 'border-right-width' |
| Style | 'border-top-style' | 'border-bottom-style' | 'border-left-style' | 'border-right-style' |
| Color | 'border-top-color' | 'border-bottom-color' | 'border-left-color' | 'border-right-color' |
The terms intrinsic width and intrinsic height refer to the width dimension and the height dimension, respectively, of intrinsic dimensions.
The basic version of the 'display' property is defined in CSS, and the property is extended by other CSS modules. [CSS] [CSSRUBY] [CSSTABLE]
The following terms and features are defined in CSS Logical Properties: [CSSLOGICAL]
The following terms and features are defined in CSS Color: [CSSCOLOR]
The term paint source is used as defined in CSS Image Values and Replaced Content to define the interaction of certain HTML elements with the CSS 'element()' function. [CSSIMAGES]
The term default object size and the 'object-fit' property are also defined in CSS Image Values and Replaced Content: [CSSIMAGES]
The following features are defined in CSS Backgrounds and Borders: [CSSBG]
The following features are defined in CSS Box Alignment: [CSSALIGN]
The following terms and features are defined in CSS Display: [CSSDISPLAY]
The following features are defined in CSS Flexible Box Layout: [CSSFLEXBOX]
The following features are defined in CSS Fonts: [CSSFONTS]
The following features are defined in CSS Grid Layout: [CSSGRID]
The following terms and features are defined in CSS Intrinsic & Extrinsic Sizing: [CSSSIZING]
The 'list-style-type' property is defined in CSS Lists and Counters. [CSSLISTS]
The following features are defined in CSS Overflow. [CSSOVERFLOW]
The following features are defined in CSS Positioned Layout: [CSSPOSITION]
The following features are defined in CSS Multi-column Layout. [CSSMULTICOL]
The 'ruby-base' value of the 'display' property is defined in CSS Ruby Layout. [CSSRUBY]
The following features are defined in CSS Table: [CSSTABLE]
The following features are defined in CSS Text: [CSSTEXT]
The following features are defined in CSS Writing Modes: [CSSWM]
The following features are defined in CSS Basic User Interface: [CSSUI]
The algorithm to update animations and send events is defined in Web Animations. [WEBANIMATIONS].
Implementations that support scripting must support the CSS Object Model. The following features and terms are defined in the CSSOM specifications: [CSSOM] [CSSOMVIEW]
Screen interfaceLinkStyle interfaceCSSStyleDeclaration interfacecssText attribute of CSSStyleDeclarationStyleSheet interfaceresize eventscroll eventThe following features and terms are defined in CSS Syntax: [CSSSYNTAX]
The following terms are defined in Selectors: [SELECTORS]
The following features are defined in CSS Values and Units: [CSSVALUES]
The term style attribute is defined in CSS Style Attributes. [CSSATTR]
The following terms are defined in the CSS Cascading and Inheritance: [CSSCASCADE]
The CanvasRenderingContext2D object's use of fonts depends on the features
described in the CSS Fonts and Font Loading specifications, including
in particular FontFace objects and the font source concept.
[CSSFONTS] [CSSFONTLOAD]
The following interfaces and terms are defined in Geometry Interfaces: [GEOMETRY]
DOMMatrix interface, and associated
m11 element,
m12 element,
m21 element,
m22 element,
m41 element, and
m42 elementDOMMatrix2DInit and
DOMMatrixInit dictionariesDOMMatrix from a dictionary
and create a DOMMatrix from a 2D dictionary
algorithms for DOMMatrix2DInit or DOMMatrixInitThe following term is defined in Intersection Observer: [INTERSECTIONOBSERVER]
The following interfaces are defined in the WebGL specifications: [WEBGL]
WebGLRenderingContext interfaceWebGL2RenderingContext interfaceWebGLContextAttributes dictionaryImplementations may support WebVTT as a text track format for subtitles, captions, metadata, etc., for media resources. [WEBVTT]
The following terms, used in this specification, are defined in WebVTT:
The following terms are defined in Fetch: [FETCH]
The following terms are defined in The WebSocket protocol: [WSP]
Sec-WebSocket-Protocol fieldThe role attribute is defined in
Accessible Rich Internet Applications (ARIA), as are the following
roles: [ARIA]
In addition, the following aria-* content
attributes are defined in ARIA: [ARIA]
Finally, the following terms are defined ARIA: [ARIA]
The following terms are defined in Content Security Policy: [CSP]
report-uri directiveframe-ancestors directivesandbox directiveThe following terms are defined in Service Workers: [SW]
The following algorithm is defined in Secure Contexts: [SECURE-CONTEXTS]
The following terms are defined in Feature Policy: [FEATUREPOLICY]
The following feature is defined in Payment Request API: [PAYMENTREQUEST]
PaymentRequest interfaceWhile support for MathML as a whole is not required by this specification (though it is encouraged, at least for Web browsers), certain features depend upon small parts of MathML being implemented. [MATHML]
The following features are defined in Mathematical Markup Language (MathML):
annotation-xml elementmath elementmerror elementmi elementmn elementmo elementms elementmtext elementWhile support for SVG as a whole is not required by this specification (though it is encouraged, at least for Web browsers), certain features depend upon parts of SVG being implemented.
User agents that implement SVG must implement the SVG 2 specification, and not any earlier revisions.
The following features are defined in the SVG 2 specification: [SVG]
SVGElement interfaceSVGImageElement interfaceSVGScriptElement interfaceSVGSVGElement interfacea elementdesc elementforeignObject elementimage elementscript elementsvg elementtitle elementuse elementThe following feature is defined in Filter Effects: [FILTERS]
The following feature is defined in Worklets: [WORKLETS]
The following features is defined in Cooperative Scheduling of Background Tasks: [REQUESTIDLECALLBACK]
This specification does not require support of any particular network protocol, style sheet language, scripting language, or any of the DOM specifications beyond those required in the list above. However, the language described by this specification is biased towards CSS as the styling language, JavaScript as the scripting language, and HTTP as the network protocol, and several features assume that those languages and protocols are in use.
A user agent that implements the HTTP protocol must implement HTTP State Management Mechanism (Cookies) as well. [HTTP] [COOKIES]
This specification might have certain additional requirements on character encodings, image formats, audio formats, and video formats in the respective sections.
Vendor-specific proprietary user agent extensions to this specification are strongly discouraged. Documents must not use such extensions, as doing so reduces interoperability and fragments the user base, allowing only users of specific user agents to access the content in question.
All extensions must be defined so that the use of extensions neither contradicts nor causes the non-conformance of functionality defined in the specification.
For example, while strongly discouraged from doing so, an implementation could add a new IDL
attribute "typeTime" to a control that returned the time it took the user
to select the current value of a control (say). On the other hand, defining a new control that
appears in a form's elements array would be in violation
of the above requirement, as it would violate the definition of elements given in this specification.
When vendor-neutral extensions to this specification are needed, either this specification can be updated accordingly, or an extension specification can be written that overrides the requirements in this specification. When someone applying this specification to their activities decides that they will recognize the requirements of such an extension specification, it becomes an applicable specification for the purposes of conformance requirements in this specification.
Someone could write a specification that defines any arbitrary byte stream as conforming, and then claim that their random junk is conforming. However, that does not mean that their random junk actually is conforming for everyone's purposes: if someone else decides that that specification does not apply to their work, then they can quite legitimately say that the aforementioned random junk is just that, junk, and not conforming at all. As far as conformance goes, what matters in a particular community is what that community agrees is applicable.
User agents must treat elements and attributes that they do not understand as semantically neutral; leaving them in the DOM (for DOM processors), and styling them according to CSS (for CSS processors), but not inferring any meaning from them.
When support for a feature is disabled (e.g. as an emergency measure to mitigate a security problem, or to aid in development, or for performance reasons), user agents must act as if they had no support for the feature whatsoever, and as if the feature was not mentioned in this specification. For example, if a particular feature is accessed via an attribute in a Web IDL interface, the attribute itself would be omitted from the objects that implement that interface — leaving the attribute on the object but making it return null or throw an exception is insufficient.
Implementations of XPath 1.0 that operate on HTML
documents parsed or created in the manners described in this specification (e.g. as part of
the document.evaluate() API) must act as if the following edit was applied
to the XPath 1.0 specification.
First, remove this paragraph:
A QName in the node test is expanded into an expanded-name using the namespace declarations from the expression context. This is the same way expansion is done for element type names in start and end-tags except that the default namespace declared with
xmlnsis not used: if the QName does not have a prefix, then the namespace URI is null (this is the same way attribute names are expanded). It is an error if the QName has a prefix for which there is no namespace declaration in the expression context.
Then, insert in its place the following:
A QName in the node test is expanded into an expanded-name using the namespace declarations from the expression context. If the QName has a prefix, then there must be a namespace declaration for this prefix in the expression context, and the corresponding namespace URI is the one that is associated with this prefix. It is an error if the QName has a prefix for which there is no namespace declaration in the expression context.
If the QName has no prefix and the principal node type of the axis is element, then the default element namespace is used. Otherwise if the QName has no prefix, the namespace URI is null. The default element namespace is a member of the context for the XPath expression. The value of the default element namespace when executing an XPath expression through the DOM3 XPath API is determined in the following way:
- If the context node is from an HTML DOM, the default element namespace is "http://www.w3.org/1999/xhtml".
- Otherwise, the default element namespace URI is null.
This is equivalent to adding the default element namespace feature of XPath 2.0 to XPath 1.0, and using the HTML namespace as the default element namespace for HTML documents. It is motivated by the desire to have implementations be compatible with legacy HTML content while still supporting the changes that this specification introduces to HTML regarding the namespace used for HTML elements, and by the desire to use XPath 1.0 rather than XPath 2.0.
This change is a willful violation of the XPath 1.0 specification, motivated by desire to have implementations be compatible with legacy content while still supporting the changes that this specification introduces to HTML regarding which namespace is used for HTML elements. [XPATH10]
XSLT 1.0 processors outputting to a DOM when the output method is "html" (either explicitly or via the defaulting rule in XSLT 1.0) are affected as follows:
If the transformation program outputs an element in no namespace, the processor must, prior to constructing the corresponding DOM element node, change the namespace of the element to the HTML namespace, ASCII-lowercase the element's local name, and ASCII-lowercase the names of any non-namespaced attributes on the element.
This requirement is a willful violation of the XSLT 1.0 specification, required because this specification changes the namespaces and case-sensitivity rules of HTML in a manner that would otherwise be incompatible with DOM-based XSLT transformations. (Processors that serialize the output are unaffected.) [XSLT10]
This specification does not specify precisely how XSLT processing interacts with the HTML
parser infrastructure (for example, whether an XSLT processor acts as if it puts any
elements into a stack of open elements). However, XSLT processors must stop
parsing if they successfully complete, and must set the current document
readiness first to "interactive" and then to "complete" if they are aborted.
This specification does not specify how XSLT interacts with the navigation algorithm, how it fits in with the event loop, nor how error pages are to be handled (e.g. whether XSLT errors are to replace an incremental XSLT output, or are rendered inline, etc).
There are also additional non-normative comments regarding the interaction of XSLT
and HTML in the script element section, and of
XSLT, XPath, and HTML in the template element
section.
Comparing two strings in a case-sensitive manner means comparing them exactly, code point for code point.
Except where otherwise stated, string comparisons must be performed in a case-sensitive manner.
A string pattern is a prefix match for a string s when pattern is not longer than s and truncating s to pattern's length leaves the two strings as matches of each other.
This document defines the following policy-controlled features:
autoplay", which has a default allowlist of 'self'.document-domain", which
has a default allowlist of *.There are various places in HTML that accept particular data types, such as dates or numbers. This section describes what the conformance criteria for content in those formats is, and how to parse them.
Implementors are strongly urged to carefully examine any third-party libraries they might consider using to implement the parsing of syntaxes described below. For example, date libraries are likely to implement error handling behavior that differs from what is required in this specification, since error-handling behavior is often not defined in specifications that describe date syntaxes similar to those used in this specification, and thus implementations tend to vary greatly in how they handle errors.
Some of the micro-parsers described below follow the pattern of having an input variable that holds the string being parsed, and having a position variable pointing at the next character to parse in input.
A number of attributes are boolean attributes. The presence of a boolean attribute on an element represents the true value, and the absence of the attribute represents the false value.
If the attribute is present, its value must either be the empty string or a value that is an ASCII case-insensitive match for the attribute's canonical name, with no leading or trailing whitespace.
The values "true" and "false" are not allowed on boolean attributes. To represent a false value, the attribute has to be omitted altogether.
Here is an example of a checkbox that is checked and disabled. The checked and disabled
attributes are the boolean attributes.
< label >< input type = checkbox checked name = cheese disabled > Cheese</ label > This could be equivalently written as this:
< label >< input type = checkbox checked = checked name = cheese disabled = disabled > Cheese</ label > You can also mix styles; the following is still equivalent:
< label >< input type = 'checkbox' checked name = cheese disabled = "" > Cheese</ label > Some attributes are defined as taking one of a finite set of keywords. Such attributes are called enumerated attributes. The keywords are each defined to map to a particular state (several keywords might map to the same state, in which case some of the keywords are synonyms of each other; additionally, some of the keywords can be said to be non-conforming, and are only in the specification for historical reasons). In addition, two default states can be given. The first is the invalid value default, the second is the missing value default.
If an enumerated attribute is specified, the attribute's value must be an ASCII case-insensitive match for one of the given keywords that are not said to be non-conforming, with no leading or trailing whitespace.
When the attribute is specified, if its value is an ASCII case-insensitive match for one of the given keywords then that keyword's state is the state that the attribute represents. If the attribute value matches none of the given keywords, but the attribute has an invalid value default, then the attribute represents that state. Otherwise, there is no default, and invalid values mean that there is no state represented.
When the attribute is not specified, if there is a missing value default state defined, then that is the state represented by the (missing) attribute. Otherwise, the absence of the attribute means that there is no state represented.
The empty string can be a valid keyword.
A string is a valid integer if it consists of one or more ASCII digits, optionally prefixed with a U+002D HYPHEN-MINUS character (-).
A valid integer without a U+002D HYPHEN-MINUS (-) prefix represents the number that is represented in base ten by that string of digits. A valid integer with a U+002D HYPHEN-MINUS (-) prefix represents the number represented in base ten by the string of digits that follows the U+002D HYPHEN-MINUS, subtracted from zero.
The rules for parsing integers are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either an integer or an error.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let sign have the value "positive".
Skip ASCII whitespace within input given position.
If position is past the end of input, return an error.
If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS character (-):
Otherwise, if the character indicated by position (the first character) is a U+002B PLUS SIGN character (+):
+" is
ignored, but it is not conforming.)If the character indicated by position is not an ASCII digit, then return an error.
Collect a sequence of code points that are ASCII digits from input given position, and interpret the resulting sequence as a base-ten integer. Let value be that integer.
If sign is "positive", return value, otherwise return the result of subtracting value from zero.
A string is a valid non-negative integer if it consists of one or more ASCII digits.
A valid non-negative integer represents the number that is represented in base ten by that string of digits.
The rules for parsing non-negative integers are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either zero, a positive integer, or an error.
Let input be the string being parsed.
Let value be the result of parsing input using the rules for parsing integers.
If value is an error, return an error.
If value is less than zero, return an error.
Return value.
A string is a valid floating-point number if it consists of:
A valid floating-point number represents the number obtained by multiplying the significand by ten raised to the power of the exponent, where the significand is the first number, interpreted as base ten (including the decimal point and the number after the decimal point, if any, and interpreting the significand as a negative number if the whole string starts with a U+002D HYPHEN-MINUS character (-) and the number is not zero), and where the exponent is the number after the E, if any (interpreted as a negative number if there is a U+002D HYPHEN-MINUS character (-) between the E and the number and the number is not zero, or else ignoring a U+002B PLUS SIGN character (+) between the E and the number if there is one). If there is no E, then the exponent is treated as zero.
The Infinity and Not-a-Number (NaN) values are not valid floating-point numbers.
The valid floating-point number concept is typically only used to
restrict what is allowed for authors, while the user agent requirements use the rules for
parsing floating-point number values below (e.g., the max attribute of the progress element). However, in
some cases the user agent requirements include checking if a string is a valid
floating-point number (e.g., the value sanitization algorithm for the Number state of the input element, or the
parse a srcset attribute algorithm).
The best representation of the number n as a floating-point number is the string obtained from running ToString(n). The abstract operation ToString is not uniquely determined. When there are multiple possible strings that could be obtained from ToString for a particular value, the user agent must always return the same string for that value (though it may differ from the value used by other user agents).
The rules for parsing floating-point number values are as given in the following algorithm. This algorithm must be aborted at the first step that returns something. This algorithm will return either a number or an error.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let value have the value 1.
Let divisor have the value 1.
Let exponent have the value 1.
Skip ASCII whitespace within input given position.
If position is past the end of input, return an error.
If the character indicated by position is a U+002D HYPHEN-MINUS character (-):
Otherwise, if the character indicated by position (the first character) is a U+002B PLUS SIGN character (+):
+"
is ignored, but it is not conforming.)If the character indicated by position is a U+002E FULL STOP (.), and that is not the last character in input, and the character after the character indicated by position is an ASCII digit, then set value to zero and jump to the step labeled fraction.
If the character indicated by position is not an ASCII digit, then return an error.
Collect a sequence of code points that are ASCII digits from input given position, and interpret the resulting sequence as a base-ten integer. Multiply value by that integer.
Fraction: If the character indicated by position is a U+002E FULL STOP (.), run these substeps:
Advance position to the next character.
If position is past the end of input, or if the character indicated by position is not an ASCII digit, U+0065 LATIN SMALL LETTER E (e), or U+0045 LATIN CAPITAL LETTER E (E), then jump to the step labeled conversion.
If the character indicated by position is a U+0065 LATIN SMALL LETTER E character (e) or a U+0045 LATIN CAPITAL LETTER E character (E), skip the remainder of these substeps.
Fraction loop: Multiply divisor by ten.
Advance position to the next character.
If position is past the end of input, then jump to the step labeled conversion.
If the character indicated by position is an ASCII digit, jump back to the step labeled fraction loop in these substeps.
If the character indicated by position is U+0065 (e) or a U+0045 (E), then:
Advance position to the next character.
If position is past the end of input, then jump to the step labeled conversion.
If the character indicated by position is a U+002D HYPHEN-MINUS character (-):
If position is past the end of input, then jump to the step labeled conversion.
Otherwise, if the character indicated by position is a U+002B PLUS SIGN character (+):
If position is past the end of input, then jump to the step labeled conversion.
If the character indicated by position is not an ASCII digit, then jump to the step labeled conversion.
Collect a sequence of code points that are ASCII digits from input given position, and interpret the resulting sequence as a base-ten integer. Multiply exponent by that integer.
Multiply value by ten raised to the exponentth power.
Conversion: Let S be the set of finite IEEE 754 double-precision floating-point values except −0, but with two special values added: 21024 and −21024.
Let rounded-value be the number in S that is closest to value, selecting the number with an even significand if there are two equally close values. (The two special values 21024 and −21024 are considered to have even significands for this purpose.)
If rounded-value is 21024 or −21024, return an error.
Return rounded-value.
The rules for parsing dimension values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a number greater than or equal to 0.0, or failure; if a number is returned, then it is further categorized as either a percentage or a length.
Let input be the string being parsed.
Let position be a position variable for input, initially pointing at the start of input.
Skip ASCII whitespace within input given position.
If position is past the end of input or the code point at position within input is not an ASCII digit, then return failure.
Collect a sequence of code points that are ASCII digits from input given position, and interpret the resulting sequence as a base-ten integer. Let value be that number.
If position is past the end of input, then return value as a length.
If the code point at position within input is U+002E (.), then:
Advance position by 1.
If position is past the end of input or the code point at position within input is not an ASCII digit, then return the current dimension value with value, input, and position.
Let divisor have the value 1.
While true:
Multiply divisor by ten.
Add the value of the code point at position within input, interpreted as a base-ten digit (0..9) and divided by divisor, to value.
Advance position by 1.
If position is past the end of input, then return value as a length.
If the code point at position within input is not an ASCII digit, then break.
Return the current dimension value with value, input, and position.
The current dimension value, given value, input, and position, is determined as follows:
If position is past the end of input, then return value as a length.
If the code point at position within input is U+0025 (%), then return value as a percentage.
Return value as a length.
The rules for parsing nonzero dimension values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a number greater than 0.0, or an error; if a number is returned, then it is further categorized as either a percentage or a length.
Let input be the string being parsed.
Let value be the result of parsing input using the rules for parsing dimension values.
If value is an error, return an error.
If value is zero, return an error.
If value is a percentage, return value as a percentage.
Return value as a length.
A valid list of floating-point numbers is a number of valid floating-point numbers separated by U+002C COMMA characters, with no other characters (e.g. no ASCII whitespace). In addition, there might be restrictions on the number of floating-point numbers that can be given, or on the range of values allowed.
The rules for parsing a list of floating-point numbers are as follows:
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let numbers be an initially empty list of floating-point numbers. This list will be the result of this algorithm.
Collect a sequence of code points that are ASCII whitespace, U+002C COMMA, or U+003B SEMICOLON characters from input given position. This skips past any leading delimiters.
While position is not past the end of input:
Collect a sequence of code points that are not ASCII whitespace, U+002C COMMA, U+003B SEMICOLON, ASCII digits, U+002E FULL STOP, or U+002D HYPHEN-MINUS characters from input given position. This skips past leading garbage.
Collect a sequence of code points that are not ASCII whitespace, U+002C COMMA, or U+003B SEMICOLON characters from input given position, and let unparsed number be the result.
Let number be the result of parsing unparsed number using the rules for parsing floating-point number values.
If number is an error, set number to zero.
Append number to numbers.
Collect a sequence of code points that are ASCII whitespace, U+002C COMMA, or U+003B SEMICOLON characters from input given position. This skips past the delimiter.
Return numbers.
The rules for parsing a list of dimensions are as follows. These rules return a list of zero or more pairs consisting of a number and a unit, the unit being one of percentage, relative, and absolute.
Let raw input be the string being parsed.
If the last character in raw input is a U+002C COMMA character (,), then remove that character from raw input.
Split the string raw input on commas. Let raw tokens be the resulting list of tokens.
Let result be an empty list of number/unit pairs.
For each token in raw tokens, run the following substeps:
Let input be the token.
Let position be a pointer into input, initially pointing at the start of the string.
Let value be the number 0.
Let unit be absolute.
If position is past the end of input, set unit to relative and jump to the last substep.
If the character at position is an ASCII digit, collect a sequence of code points that are ASCII digits from input given position, interpret the resulting sequence as an integer in base ten, and increment value by that integer.
If the character at position is U+002E (.), then:
Collect a sequence of code points consisting of ASCII whitespace and ASCII digits from input given position. Let s be the resulting sequence.
Remove all ASCII whitespace in s.
If s is not the empty string, then:
Let length be the number of characters in s (after the spaces were removed).
Let fraction be the result of interpreting s as a base-ten integer, and then dividing that number by 10length.
Increment value by fraction.
Skip ASCII whitespace within input given position.
If the character at position is a U+0025 PERCENT SIGN character (%), then set unit to percentage.
Otherwise, if the character at position is a U+002A ASTERISK character (*), then set unit to relative.
Add an entry to result consisting of the number given by value and the unit given by unit.
Return the list result.
In the algorithms below, the number of days in month month of year year is: 31 if month is 1, 3, 5, 7, 8, 10, or 12; 30 if month is 4, 6, 9, or 11; 29 if month is 2 and year is a number divisible by 400, or if year is a number divisible by 4 but not by 100; and 28 otherwise. This takes into account leap years in the Gregorian calendar. [GREGORIAN]
When ASCII digits are used in the date and time syntaxes defined in this section, they express numbers in base ten.
While the formats described here are intended to be subsets of the corresponding ISO8601 formats, this specification defines parsing rules in much more detail than ISO8601. Implementors are therefore encouraged to carefully examine any date parsing libraries before using them to implement the parsing rules described below; ISO8601 libraries might not parse dates and times in exactly the same manner. [ISO8601]
Where this specification refers to the proleptic Gregorian calendar, it means the modern Gregorian calendar, extrapolated backwards to year 1. A date in the proleptic Gregorian calendar, sometimes explicitly referred to as a proleptic-Gregorian date, is one that is described using that calendar even if that calendar was not in use at the time (or place) in question. [GREGORIAN]
The use of the Gregorian calendar as the wire format in this specification is an
arbitrary choice resulting from the cultural biases of those involved in the decision. See also
the section discussing date, time, and number formats in forms
(for authors), implementation notes regarding
localization of form controls, and the time element.
A month consists of a specific proleptic-Gregorian date with no time-zone information and no date information beyond a year and a month. [GREGORIAN]
A string is a valid month string representing a year year and month month if it consists of the following components in the given order:
The rules to parse a month string are as follows. This will return either a year and month, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a month component to obtain year and month. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Return year and month.
The rules to parse a month component, given an input string and a position, are as follows. This will return either a year and a month, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the year.
If year is not a number greater than zero, then fail.
If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the month.
If month is not a number in the range 1 ≤ month ≤ 12, then fail.
Return year and month.
A date consists of a specific proleptic-Gregorian date with no time-zone information, consisting of a year, a month, and a day. [GREGORIAN]
A string is a valid date string representing a year year, month month, and day day if it consists of the following components in the given order:
The rules to parse a date string are as follows. This will return either a date, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Let date be the date with year year, month month, and day day.
Return date.
The rules to parse a date component, given an input string and a position, are as follows. This will return either a year, a month, and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Parse a month component to obtain year and month. If this returns nothing, then fail.
Let maxday be the number of days in month month of year year.
If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the day.
If day is not a number in the range 1 ≤ day ≤ maxday, then fail.
Return year, month, and day.
A yearless date consists of a Gregorian month and a day within that month, but with no associated year. [GREGORIAN]
A string is a valid yearless date string representing a month month and a day day if it consists of the following components in the given order:
In other words, if the month is "02",
meaning February, then the day can be 29, as if the year was a leap year.
The rules to parse a yearless date string are as follows. This will return either a month and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a yearless date component to obtain month and day. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Return month and day.
The rules to parse a yearless date component, given an input string and a position, are as follows. This will return either a month and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Collect a sequence of code points that are U+002D HYPHEN-MINUS characters (-) from input given position. If the collected sequence is not exactly zero or two characters long, then fail.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the month.
If month is not a number in the range 1 ≤ month ≤ 12, then fail.
Let maxday be the number of days in month month of any arbitrary leap year (e.g. 4 or 2000).
If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the day.
If day is not a number in the range 1 ≤ day ≤ maxday, then fail.
Return month and day.
A time consists of a specific time with no time-zone information, consisting of an hour, a minute, a second, and a fraction of a second.
A string is a valid time string representing an hour hour, a minute minute, and a second second if it consists of the following components in the given order:
The second component cannot be 60 or 61; leap seconds cannot be represented.
The rules to parse a time string are as follows. This will return either a time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Let time be the time with hour hour, minute minute, and second second.
Return time.
The rules to parse a time component, given an input string and a position, are as follows. This will return either an hour, a minute, and a second, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the hour.
If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the minute.
Let second be 0.
If position is not beyond the end of input and the character at position is U+003A (:), then:
Advance position to the next character in input.
If position is beyond the end of input, or at the last character in input, or if the next two characters in input starting at position are not both ASCII digits, then fail.
Collect a sequence of code points that are either ASCII digits or U+002E FULL STOP characters from input given position. If the collected sequence is three characters long, or if it is longer than three characters long and the third character is not a U+002E FULL STOP character, or if it has more than one U+002E FULL STOP character, then fail. Otherwise, interpret the resulting sequence as a base-ten number (possibly with a fractional part). Set second to that number.
If second is not a number in the range 0 ≤ second < 60, then fail.
Return hour, minute, and second.
A local date and time consists of a specific proleptic-Gregorian date, consisting of a year, a month, and a day, and a time, consisting of an hour, a minute, a second, and a fraction of a second, but expressed without a time zone. [GREGORIAN]
A string is a valid local date and time string representing a date and time if it consists of the following components in the given order:
A string is a valid normalized local date and time string representing a date and time if it consists of the following components in the given order:
The rules to parse a local date and time string are as follows. This will return either a date and time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
If position is beyond the end of input or if the character at position is neither a U+0054 LATIN CAPITAL LETTER T character (T) nor a U+0020 SPACE character, then fail. Otherwise, move position forwards one character.
Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Let date be the date with year year, month month, and day day.
Let time be the time with hour hour, minute minute, and second second.
Return date and time.
A time-zone offset consists of a signed number of hours and minutes.
A string is a valid time-zone offset string representing a time-zone offset if it consists of either:
A U+005A LATIN CAPITAL LETTER Z character (Z), allowed only if the time zone is UTC
Or, the following components, in the given order:
This format allows for time-zone offsets from -23:59 to +23:59. Right now, in practice, the range of offsets of actual time zones is -12:00 to +14:00, and the minutes component of offsets of actual time zones is always either 00, 30, or 45. There is no guarantee that this will remain so forever, however, since time zones are used as political footballs and are thus subject to very whimsical policy decisions.
See also the usage notes and examples in the global date and time section below for details on using time-zone offsets with historical times that predate the formation of formal time zones.
The rules to parse a time-zone offset string are as follows. This will return either a time-zone offset, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a time-zone offset component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Return the time-zone offset that is timezonehours hours and timezoneminutes minutes from UTC.
The rules to parse a time-zone offset component, given an input string and a position, are as follows. This will return either time-zone hours and time-zone minutes, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
If the character at position is a U+005A LATIN CAPITAL LETTER Z character (Z), then:
Let timezonehours be 0.
Let timezoneminutes be 0.
Advance position to the next character in input.
Otherwise, if the character at position is either a U+002B PLUS SIGN (+) or a U+002D HYPHEN-MINUS (-), then:
If the character at position is a U+002B PLUS SIGN (+), let sign be "positive". Otherwise, it's a U+002D HYPHEN-MINUS (-); let sign be "negative".
Advance position to the next character in input.
Collect a sequence of code points that are ASCII digits from input given position. Let s be the collected sequence.
If s is exactly two characters long, then:
Interpret s as a base-ten integer. Let that number be the timezonehours.
If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the timezoneminutes.
If s is exactly four characters long, then:
Interpret the first two characters of s as a base-ten integer. Let that number be the timezonehours.
Interpret the last two characters of s as a base-ten integer. Let that number be the timezoneminutes.
Otherwise, fail.
Otherwise, fail.
Return timezonehours and timezoneminutes.
A global date and time consists of a specific proleptic-Gregorian date, consisting of a year, a month, and a day, and a time, consisting of an hour, a minute, a second, and a fraction of a second, expressed with a time-zone offset, consisting of a signed number of hours and minutes. [GREGORIAN]
A string is a valid global date and time string representing a date, time, and a time-zone offset if it consists of the following components in the given order:
Times in dates before the formation of UTC in the mid twentieth century must be expressed and interpreted in terms of UT1 (contemporary Earth solar time at the 0° longitude), not UTC (the approximation of UT1 that ticks in SI seconds). Time before the formation of time zones must be expressed and interpreted as UT1 times with explicit time zones that approximate the contemporary difference between the appropriate local time and the time observed at the location of Greenwich, London.
The following are some examples of dates written as valid global date and time strings.
0037-12-13 00:00Z"1979-10-14T12:00:00.001-04:00"8592-01-01T02:09+02:09"Several things are notable about these dates:
T" is replaced by a space, it must be a single space
character. The string "2001-12-21 12:00Z" (with two spaces
between the components) would not be parsed successfully.The rules to parse a global date and time string are as follows. This will return either a time in UTC, with associated time-zone offset information for round-tripping or display purposes, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
If position is beyond the end of input or if the character at position is neither a U+0054 LATIN CAPITAL LETTER T character (T) nor a U+0020 SPACE character, then fail. Otherwise, move position forwards one character.
Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
If position is beyond the end of input, then fail.
Parse a time-zone offset component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
Let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezonehours hours and timezoneminutes minutes. That moment in time is a moment in the UTC time zone.
Let timezone be timezonehours hours and timezoneminutes minutes from UTC.
Return time and timezone.
A week consists of a week-year number and a week number representing a seven-day period starting on a Monday. Each week-year in this calendaring system has either 52 or 53 such seven-day periods, as defined below. The seven-day period starting on the Gregorian date Monday December 29th 1969 (1969-12-29) is defined as week number 1 in week-year 1970. Consecutive weeks are numbered sequentially. The week before the number 1 week in a week-year is the last week in the previous week-year, and vice versa. [GREGORIAN]
A week-year with a number year has 53 weeks if it corresponds to either a year year in the proleptic Gregorian calendar that has a Thursday as its first day (January 1st), or a year year in the proleptic Gregorian calendar that has a Wednesday as its first day (January 1st) and where year is a number divisible by 400, or a number divisible by 4 but not by 100. All other week-years have 52 weeks.
The week number of the last day of a week-year with 53 weeks is 53; the week number of the last day of a week-year with 52 weeks is 52.
The week-year number of a particular day can be different than the number of the year that contains that day in the proleptic Gregorian calendar. The first week in a week-year y is the week that contains the first Thursday of the Gregorian year y.
For modern purposes, a week as defined here is equivalent to ISO weeks as defined in ISO 8601. [ISO8601]
A string is a valid week string representing a week-year year and week week if it consists of the following components in the given order:
The rules to parse a week string are as follows. This will return either a week-year number and week number, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the year.
If year is not a number greater than zero, then fail.
If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.
If position is beyond the end of input or if the character at position is not a U+0057 LATIN CAPITAL LETTER W character (W), then fail. Otherwise, move position forwards one character.
Collect a sequence of code points that are ASCII digits from input given position. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the week.
Let maxweek be the week number of the last day of year year.
If week is not a number in the range 1 ≤ week ≤ maxweek, then fail.
If position is not beyond the end of input, then fail.
Return the week-year number year and the week number week.
A duration consists of a number of seconds.
Since months and seconds are not comparable (a month is not a precise number of seconds, but is instead a period whose exact length depends on the precise day from which it is measured) a duration as defined in this specification cannot include months (or years, which are equivalent to twelve months). Only durations that describe a specific number of seconds can be described.
A string is a valid duration string representing a duration t if it consists of either of the following:
A literal U+0050 LATIN CAPITAL LETTER P character followed by one or more of the following subcomponents, in the order given, where the number of days, hours, minutes, and seconds corresponds to the same number of seconds as in t:
One or more ASCII digits followed by a U+0044 LATIN CAPITAL LETTER D character, representing a number of days.
A U+0054 LATIN CAPITAL LETTER T character followed by one or more of the following subcomponents, in the order given:
One or more ASCII digits followed by a U+0048 LATIN CAPITAL LETTER H character, representing a number of hours.
One or more ASCII digits followed by a U+004D LATIN CAPITAL LETTER M character, representing a number of minutes.
The following components:
One or more ASCII digits, representing a number of seconds.
Optionally, a U+002E FULL STOP character (.) followed by one, two, or three ASCII digits, representing a fraction of a second.
A U+0053 LATIN CAPITAL LETTER S character.
This, as with a number of other date- and time-related microsyntaxes defined in this specification, is based on one of the formats defined in ISO 8601. [ISO8601]
One or more duration time components, each with a different duration time component scale, in any order; the sum of the represented seconds being equal to the number of seconds in t.
A duration time component is a string consisting of the following components:
Zero or more ASCII whitespace.
One or more ASCII digits, representing a number of time units, scaled by the duration time component scale specified (see below) to represent a number of seconds.
If the duration time component scale specified is 1 (i.e. the units are seconds), then, optionally, a U+002E FULL STOP character (.) followed by one, two, or three ASCII digits, representing a fraction of a second.
Zero or more ASCII whitespace.
One of the following characters, representing the duration time component scale of the time unit used in the numeric part of the duration time component:
Zero or more ASCII whitespace.
This is not based on any of the formats in ISO 8601. It is intended to be a more human-readable alternative to the ISO 8601 duration format.
The rules to parse a duration string are as follows. This will return either a duration or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Let months, seconds, and component count all be zero.
Let M-disambiguator be minutes.
This flag's other value is months. It is used to disambiguate the "M" unit in ISO8601 durations, which use the same unit for months and minutes. Months are not allowed, but are parsed for future compatibility and to avoid misinterpreting ISO8601 durations that would be valid in other contexts.
Skip ASCII whitespace within input given position.
If position is past the end of input, then fail.
If the character in input pointed to by position is a U+0050 LATIN CAPITAL LETTER P character, then advance position to the next character, set M-disambiguator to months, and skip ASCII whitespace within input given position.
While true:
Let units be undefined. It will be assigned one of the following values: years, months, weeks, days, hours, minutes, and seconds.
Let next character be undefined. It is used to process characters from the input.
If position is past the end of input, then break.
If the character in input pointed to by position is a U+0054 LATIN CAPITAL LETTER T character, then advance position to the next character, set M-disambiguator to minutes, skip ASCII whitespace within input given position, and continue.
Set next character to the character in input pointed to by position.
If next character is a U+002E FULL STOP character (.), then let N equal zero. (Do not advance position. That is taken care of below.)
Otherwise, if next character is an ASCII digit, then collect a sequence of code points that are ASCII digits from input given position, interpret the resulting sequence as a base-ten integer, and let N be that number.
Otherwise next character is not part of a number; fail.
If position is past the end of input, then fail.
Set next character to the character in input pointed to by position, and this time advance position to the next character. (If next character was a U+002E FULL STOP character (.) before, it will still be that character this time.)
If next character is U+002E (.), then:
Collect a sequence of code points that are ASCII digits from input given position. Let s be the resulting sequence.
If s is the empty string, then fail.
Let length be the number of characters in s.
Let fraction be the result of interpreting s as a base-ten integer, and then dividing that number by 10length.
Increment N by fraction.
Skip ASCII whitespace within input given position.
If position is past the end of input, then fail.
Set next character to the character in input pointed to by position, and advance position to the next character.
If next character is neither a U+0053 LATIN CAPITAL LETTER S character nor a U+0073 LATIN SMALL LETTER S character, then fail.
Set units to seconds.
Otherwise:
If next character is ASCII whitespace, then skip ASCII whitespace within input given position, set next character to the character in input pointed to by position, and advance position to the next character.
If next character is a U+0059 LATIN CAPITAL LETTER Y character, or a U+0079 LATIN SMALL LETTER Y character, set units to years and set M-disambiguator to months.
If next character is a U+004D LATIN CAPITAL LETTER M character or a U+006D LATIN SMALL LETTER M character, and M-disambiguator is months, then set units to months.
If next character is a U+0057 LATIN CAPITAL LETTER W character or a U+0077 LATIN SMALL LETTER W character, set units to weeks and set M-disambiguator to minutes.
If next character is a U+0044 LATIN CAPITAL LETTER D character or a U+0064 LATIN SMALL LETTER D character, set units to days and set M-disambiguator to minutes.
If next character is a U+0048 LATIN CAPITAL LETTER H character or a U+0068 LATIN SMALL LETTER H character, set units to hours and set M-disambiguator to minutes.
If next character is a U+004D LATIN CAPITAL LETTER M character or a U+006D LATIN SMALL LETTER M character, and M-disambiguator is minutes, then set units to minutes.
If next character is a U+0053 LATIN CAPITAL LETTER S character or a U+0073 LATIN SMALL LETTER S character, set units to seconds and set M-disambiguator to minutes.
Otherwise if next character is none of the above characters, then fail.
Increment component count.
Let multiplier be 1.
If units is years, multiply multiplier by 12 and set units to months.
If units is months, add the product of N and multiplier to months.
Otherwise:
If units is weeks, multiply multiplier by 7 and set units to days.
If units is days, multiply multiplier by 24 and set units to hours.
If units is hours, multiply multiplier by 60 and set units to minutes.
If units is minutes, multiply multiplier by 60 and set units to seconds.
Forcibly, units is now seconds. Add the product of N and multiplier to seconds.
Skip ASCII whitespace within input given position.
If component count is zero, fail.
If months is not zero, fail.
Return the duration consisting of seconds seconds.
A string is a valid date string with optional time if it is also one of the following:
The rules to parse a date or time string are as follows. The algorithm will return either a date, a time, a global date and time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
Let input be the string being parsed.
Let position be a pointer into input, initially pointing at the start of the string.
Set start position to the same position as position.
Set the date present and time present flags to true.
Parse a date component to obtain year, month, and day. If this fails, then set the date present flag to false.
If date present is true, and position is not beyond the end of input, and the character at position is either a U+0054 LATIN CAPITAL LETTER T character (T) or a U+0020 SPACE character, then advance position to the next character in input.
Otherwise, if date present is true, and either position is beyond the end of input or the character at position is neither a U+0054 LATIN CAPITAL LETTER T character (T) nor a U+0020 SPACE character, then set time present to false.
Otherwise, if date present is false, set position back to the same position as start position.
If the time present flag is true, then parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
If the date present and time present flags are both true, but position is beyond the end of input, then fail.
If the date present and time present flags are both true, parse a time-zone offset component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.
If position is not beyond the end of input, then fail.
If the date present flag is true and the time present flag is false, then let date be the date with year year, month month, and day day, and return date.
Otherwise, if the time present flag is true and the date present flag is false, then let time be the time with hour hour, minute minute, and second second, and return time.
Otherwise, let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezonehours hours and timezoneminutes minutes, that moment in time being a moment in the UTC time zone; let timezone be timezonehours hours and timezoneminutes minutes from UTC; and return time and timezone.
A simple color consists of three 8-bit numbers in the range 0..255, representing the red, green, and blue components of the color respectively, in the sRGB color space. [SRGB]
A string is a valid simple color if it is exactly seven characters long, and the first character is a U+0023 NUMBER SIGN character (#), and the remaining six characters are all ASCII hex digits, with the first two digits representing the red component, the middle two digits representing the green component, and the last two digits representing the blue component, in hexadecimal.
A string is a valid lowercase simple color if it is a valid simple color and doesn't use any characters in the range U+0041 LATIN CAPITAL LETTER A to U+0046 LATIN CAPITAL LETTER F.
The rules for parsing simple color values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a simple color or an error.
Let input be the string being parsed.
If input is not exactly seven characters long, then return an error.
If the first character in input is not a U+0023 NUMBER SIGN character (#), then return an error.
If the last six characters of input are not all ASCII hex digits, then return an error.
Let result be a simple color.
Interpret the second and third characters as a hexadecimal number and let the result be the red component of result.
Interpret the fourth and fifth characters as a hexadecimal number and let the result be the green component of result.
Interpret the sixth and seventh characters as a hexadecimal number and let the result be the blue component of result.
Return result.
The rules for serializing simple color values given a simple color are as given in the following algorithm:
Let result be a string consisting of a single U+0023 NUMBER SIGN character (#).
Convert the red, green, and blue components in turn to two-digit hexadecimal numbers using ASCII lower hex digits, zero-padding if necessary, and append these numbers to result, in the order red, green, blue.
Return result, which will be a valid lowercase simple color.
Some obsolete legacy attributes parse colors in a more complicated manner, using the rules for parsing a legacy color value, which are given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a simple color or an error.
Let input be the string being parsed.
If input is the empty string, then return an error.
Strip leading and trailing ASCII whitespace from input.
If input is an ASCII case-insensitive match for the
string "transparent", then return an error.
If input is an ASCII case-insensitive match for one of the named colors, then return the simple color corresponding to that keyword. [CSSCOLOR]
CSS2 System Colors are not recognized.
If input is four characters long, and the first character in input is U+0023 (#), and the last three characters of input are all ASCII hex digits, then:
Let result be a simple color.
Interpret the second character of input as a hexadecimal digit; let the red component of result be the resulting number multiplied by 17.
Interpret the third character of input as a hexadecimal digit; let the green component of result be the resulting number multiplied by 17.
Interpret the fourth character of input as a hexadecimal digit; let the blue component of result be the resulting number multiplied by 17.
Return result.
Replace any characters in input that have a code point greater than U+FFFF
(i.e., any characters that are not in the basic multilingual plane) with the two-character string
"00".
If input is longer than 128 characters, truncate input, leaving only the first 128 characters.
If the first character in input is a U+0023 NUMBER SIGN character (#), remove it.
Replace any character in input that is not an ASCII hex digit with the character U+0030 DIGIT ZERO (0).
While input's length is zero or not a multiple of three, append a U+0030 DIGIT ZERO (0) character to input.
Split input into three strings of equal length, to obtain three components. Let length be the length of those components (one third the length of input).
If length is greater than 8, then remove the leading length-8 characters in each component, and let length be 8.
While length is greater than two and the first character in each component is a U+0030 DIGIT ZERO (0) character, remove that character and reduce length by one.
If length is still greater than two, truncate each component, leaving only the first two characters in each.
Let result be a simple color.
Interpret the first component as a hexadecimal number; let the red component of result be the resulting number.
Interpret the second component as a hexadecimal number; let the green component of result be the resulting number.
Interpret the third component as a hexadecimal number; let the blue component of result be the resulting number.
Return result.
The 2D graphics context has a separate color syntax that also handles opacity.
A set of space-separated tokens is a string containing zero or more words (known as tokens) separated by one or more ASCII whitespace, where words consist of any string of one or more characters, none of which are ASCII whitespace.
A string containing a set of space-separated tokens may have leading or trailing ASCII whitespace.
An unordered set of unique space-separated tokens is a set of space-separated tokens where none of the tokens are duplicated.
An ordered set of unique space-separated tokens is a set of space-separated tokens where none of the tokens are duplicated but where the order of the tokens is meaningful.
Sets of space-separated tokens sometimes have a defined set of allowed values. When a set of allowed values is defined, the tokens must all be from that list of allowed values; other values are non-conforming. If no such set of allowed values is provided, then all values are conforming.
How tokens in a set of space-separated tokens are to be compared (e.g. case-sensitively or not) is defined on a per-set basis.
A set of comma-separated tokens is a string containing zero or more tokens each separated from the next by a single U+002C COMMA character (,), where tokens consist of any string of zero or more characters, neither beginning nor ending with ASCII whitespace, nor containing any U+002C COMMA characters (,), and optionally surrounded by ASCII whitespace.
For instance, the string " a ,b,,d d " consists of four tokens: "a", "b", the empty
string, and "d d". Leading and trailing whitespace around each token doesn't count as part of
the token, and the empty string can be a token.
Sets of comma-separated tokens sometimes have further restrictions on what consists a valid token. When such restrictions are defined, the tokens must all fit within those restrictions; other values are non-conforming. If no such restrictions are specified, then all values are conforming.
A valid hash-name reference to an element of type type is a
string consisting of a U+0023 NUMBER SIGN character (#) followed by a string which exactly matches
the value of the name attribute of an element with type type in
the same tree.
The rules for parsing a hash-name reference to an element of type type, given a context node scope, are as follows:
If the string being parsed does not contain a U+0023 NUMBER SIGN character, or if the first such character in the string is the last character in the string, then return null.
Let s be the string from the character immediately after the first U+0023 NUMBER SIGN character in the string being parsed up to the end of that string.
Return the first element of type type in scope's tree, in
tree order, that has an id or name attribute whose value is s, or null if there is no such
element.
Although id attributes are accounted for when
parsing, they are not used in determining whether a value is a valid hash-name
reference. That is, a hash-name reference that refers to an element based on id is a conformance error (unless that element also has a name attribute with the same value).
A string is a valid media query list if it matches the <media-query-list> production of Media Queries. [MQ]
A string matches the environment of the user if it is the empty string, a string consisting of only ASCII whitespace, or is a media query list that matches the user's environment according to the definitions given in Media Queries. [MQ]
A string is a valid non-empty URL if it is a valid URL string but it is not the empty string.
A string is a valid URL potentially surrounded by spaces if, after stripping leading and trailing ASCII whitespace from it, it is a valid URL string.
A string is a valid non-empty URL potentially surrounded by spaces if, after stripping leading and trailing ASCII whitespace from it, it is a valid non-empty URL.
This specification defines the URL about:legacy-compat as a reserved,
though unresolvable, about: URL, for use in DOCTYPEs in HTML documents when needed for
compatibility with XML tools. [ABOUT]
This specification defines the URL about:html-kind as a reserved,
though unresolvable, about: URL, that is used as an
identifier for kinds of media tracks. [ABOUT]
This specification defines the URL about:srcdoc as a reserved, though
unresolvable, about: URL, that is used as the URL of iframe srcdoc documents.
[ABOUT]
The fallback base URL of a Document object document is the
URL record obtained by running these steps:
If document is an iframe srcdoc document, then return the document base
URL of document's browsing context's
browsing context container's node document.
If document's URL is
about:blank, and document's browsing
context's creator base URL is non-null, then return that creator base
URL.
Return document's URL.
The document base URL of a Document object is the
absolute URL obtained by running these steps:
If there is no base element that has an href attribute in the Document, then return the
Document's fallback base URL.
Otherwise, return the frozen base URL of the first base element
in the Document that has an href attribute, in
tree order.
Parsing a URL is the process of taking a string and obtaining the URL record that it represents. While this process is defined in URL, the HTML standard defines a wrapper for convenience. [URL]
This wrapper is only useful when the character encoding for the URL parser has to match that of the document or environment settings object for legacy reasons. When that is not the case the URL parser can be used directly.
To parse a URL url, relative to either a document or environment settings object, the user agent must use the following steps. Parsing a URL either results in failure or a resulting URL string and resulting URL record.
Let encoding be document's character encoding, if document was given, and environment settings object's API URL character encoding otherwise.
Let baseURL be document's base URL, if document was given, and environment settings object's API base URL otherwise.
Let urlRecord be the result of applying the URL parser to url, with baseURL and encoding.
If urlRecord is failure, then return failure.
Let urlString be the result of applying the URL serializer to urlRecord.
Return urlString as the resulting URL string and urlRecord as the resulting URL record.
When a document's document base URL changes, all elements in that document are affected by a base URL change.
The following are base URL change steps, which run when an element is affected by a base URL change (as defined by DOM):
If the URL identified by the hyperlink is being shown to the user, or if any
data derived from that URL is affecting the display, then the href attribute should be reparsed relative to the element's node document and the UI updated
appropriately.
For example, the CSS :link/:visited pseudo-classes
might have been affected.
If the hyperlink has a ping attribute and its
URL(s) are being shown to the user, then the ping attribute's tokens should be reparsed relative to the element's node document and the UI updated
appropriately.
q, blockquote, ins, or
del element with a cite attributeIf the URL identified by the cite attribute is being
shown to the user, or if any data derived from that URL is affecting the display,
then the URL should be reparsed relative to the
element's node document and the UI updated appropriately.
The element is not directly affected.
For instance, changing the base URL doesn't affect the image displayed by
img elements, although subsequent accesses of the src IDL attribute from script will return a new absolute
URL that might no longer correspond to the image being shown.
A response whose type is "basic", "cors", or "default" is CORS-same-origin. [FETCH]
A response whose type is "opaque" or "opaqueredirect" is CORS-cross-origin.
A response's unsafe response is its internal response if it has one, and the response itself otherwise.
To create a potential-CORS request, given a url, destination, corsAttributeState, and an optional same-origin fallback flag, run these steps:
Let mode be "no-cors" if corsAttributeState
is No CORS, and "cors"
otherwise.
If same-origin fallback flag is set and mode is "no-cors", set mode to "same-origin".
Let credentialsMode be "include".
If corsAttributeState is Anonymous, set credentialsMode to "same-origin".
Let request be a new request whose url is url, destination is destination, mode is mode, credentials mode is credentialsMode, and whose use-URL-credentials flag is set.
The Content-Type metadata of a resource must be obtained and interpreted in a manner consistent with the requirements of MIME Sniffing. [MIMESNIFF]
The computed MIME type of a resource must be found in a manner consistent with the requirements given in MIME Sniffing. [MIMESNIFF]
The rules for sniffing images specifically, the rules for distinguishing if a resource is text or binary, and the rules for sniffing audio and video specifically are also defined in MIME Sniffing. These rules return a MIME type as their result. [MIMESNIFF]
It is imperative that the rules in MIME Sniffing be followed exactly. When a user agent uses different heuristics for content type detection than the server expects, security problems can occur. For more details, see MIME Sniffing. [MIMESNIFF]
meta elementsThe algorithm for extracting a character encoding from a meta element,
given a string s, is as follows. It either returns a character encoding or
nothing.
Let position be a pointer into s, initially pointing at the start of the string.
Loop: Find the first seven characters in s after position that are an ASCII case-insensitive match for the word "charset". If no such match is found, return nothing.
Skip any ASCII whitespace that immediately follow the word "charset" (there might not be any).
If the next character is not a U+003D EQUALS SIGN (=), then move position to point just before that next character, and jump back to the step labeled loop.
Skip any ASCII whitespace that immediately follow the equals sign (there might not be any).
Process the next character as follows:
This algorithm is distinct from those in the HTTP specifications (for example, HTTP doesn't allow the use of single quotes and requires supporting a backslash-escape mechanism that is not supported by this algorithm). While the algorithm is used in contexts that, historically, were related to HTTP, the syntax as supported by implementations diverged some time ago. [HTTP]
A CORS settings attribute is an enumerated attribute. The following table lists the keywords and states for the attribute — the keywords in the left column map to the states in the cell in the second column on the same row as the keyword.
| Keyword | State | Brief description |
|---|---|---|
anonymous
| Anonymous | Requests for the element will have their mode set to "cors" and their credentials mode set to "same-origin".
|
use-credentials
| Use Credentials | Requests for the element will have their mode set to "cors" and their credentials mode set to "include".
|
The empty string is also a valid keyword, and maps to the Anonymous state. The attribute's invalid value default is the Anonymous state. For the
purposes of reflection, the canonical case for the Anonymous state is the anonymous keyword. The missing value default, used when the attribute is omitted, is the No
CORS state.
The majority of fetches governed by CORS settings attributes will be done via the create a potential-CORS request algorithm.
For module scripts, certain CORS settings attributes have been repurposed to have a slightly different
meaning, wherein they only impact the request's credentials mode (since the mode is always "cors"). To perform
this translation, we define the module script credentials mode for a given CORS
settings attribute to be determined by switching on the attribute's state:
same-origin"include"A referrer policy attribute is an enumerated attribute. Each referrer policy, including the empty string, is a keyword for this attribute, mapping to a state of the same name.
The attribute's invalid value default and missing value default are both the empty string state.
The impact of these states on the processing model of various fetches is defined in more detail throughout this specification, in Fetch, and in Referrer Policy. [FETCH] [REFERRERPOLICY]
Several signals can contribute to which processing model is used for a given fetch; a referrer policy attribute is only one of them. In general, the order in which these signals are processed are:
First, the presence of a noreferrer link
type;
Then, the value of a referrer policy attribute;
Then, the presence of any meta element with name attribute set to referrer.
Finally, the `Referrer-Policy` HTTP
header.
A nonce content attribute represents a cryptographic nonce ("number used once") which can be used by Content Security Policy to determine whether or not a given fetch will be allowed to proceed. The value is text. [CSP]
Elements that have a nonce content attribute ensure that the
crytographic nonce is only exposed to script (and not to side-channels like CSS attribute
selectors) by extracting the value from the content attribute, moving it into an internal slot
named [[CryptographicNonce]], and exposing it to script via the
HTMLOrSVGElement interface mixin. Unless otherwise specified, the slot's value
is the empty string.
nonceReturns the value of the element's [[CryptographicNonce]] internal slot.
Can be set, to update that slot's value.
The nonce IDL
attribute must, on getting, return the value of this element's
[[CryptographicNonce]]; and on setting, set this element's
[[CryptographicNonce]] to the given value.
Note how the setter for the nonce IDL attribute does not update the corresponding
content attribute. This, as well as the below setting of the nonce content attribute to the empty string when an element
becomes browsing-context connected, is meant to prevent exfiltration of the nonce
value through mechanisms that can easily read content attributes, such as selectors. Learn more in
issue #2369, where this behavior was
introduced.
Whenever an element including HTMLOrSVGElement has its nonce attribute is set or changed, set this element's
[[CryptographicNonce]] to the given value.
Whenever an element including HTMLOrSVGElement becomes browsing-context
connected, the user agent must execute the following steps on the element:
Let CSP list be element's shadow-including root's CSP list.
If CSP list contains a header-delivered Content Security Policy, and
element has a nonce content attribute
attr whose value is not the empty string, then:
Set an attribute value for
element using "nonce" and the empty
string.
As each Document's CSP
list is append-only, user agents can optimize away the contains a header-delivered
Content Security Policy check by, for example, holding a flag on the Document,
set during Document
creation and initialization.
The cloning steps for elements that include
HTMLOrSVGElement must set the [[CryptographicNonce]] slot on the copy
to the value of the slot on the element being cloned.
Some IDL attributes are defined to reflect a particular content attribute. This means that on getting, the IDL attribute returns the current value of the content attribute, and on setting, the IDL attribute changes the value of the content attribute to the given value.
In general, on getting, if the content attribute is not present, the IDL attribute must act as if the content attribute's value is the empty string; and on setting, if the content attribute is not present, it must first be added.
If a reflecting IDL attribute is a USVString attribute
whose content attribute is defined to contain a URL, then on getting, if the
content attribute is absent, the IDL attribute must return the empty string. Otherwise, the IDL
attribute must parse the value of the content attribute relative
to the element's node document and if that is successful, return the resulting
URL string. If parsing fails, then the value of the content attribute must be returned
instead, converted to a USVString. On setting, the content attribute must be set to the
specified new value.
If a reflecting IDL attribute is a DOMString attribute
whose content attribute is an enumerated attribute, and the IDL attribute is
limited to only known values, then, on getting, the IDL attribute must return the
conforming value associated with the state the attribute is in (in its canonical case), if any, or
the empty string if the attribute is in a state that has no associated keyword value or if the
attribute is not in a defined state (e.g. the attribute is missing and there is no missing value default). On setting, the content attribute must
be set to the specified new value.
If a reflecting IDL attribute is a nullable DOMString
attribute whose content attribute is an enumerated attribute, then, on getting, if
the corresponding content attribute is in its missing value default then the IDL attribute
must return null, otherwise, the IDL attribute must return the conforming value associated with
the state the attribute is in (in its canonical case). On setting, if the new value is null, the
content attribute must be removed, and otherwise, the content attribute must be set to the
specified new value.
If a reflecting IDL attribute is a DOMString or USVString attribute but doesn't fall into any of the above
categories, then the getting and setting must be done in a transparent, case-preserving manner.
If a reflecting IDL attribute is a boolean attribute, then on
getting the IDL attribute must return true if the content attribute is set, and false if it is
absent. On setting, the content attribute must be removed if the IDL attribute is set to false,
and must be set to the empty string if the IDL attribute is set to true. (This corresponds to the
rules for boolean content attributes.)
If a reflecting IDL attribute has a signed integer type (long)
then, on getting, the content attribute must be parsed according to the rules for parsing signed integers, and if that is successful, and the
value is in the range of the IDL attribute's type, the resulting value must be returned. If, on
the other hand, it fails or returns an out of range value, or if the attribute is absent, then the
default value must be returned instead, or 0 if there is no default value. On setting, the given
value must be converted to the shortest possible string representing the number as a valid
integer and then that string must be used as the new content attribute value.
If a reflecting IDL attribute has a signed integer type (long)
that is limited to only non-negative numbers then, on getting, the content attribute
must be parsed according to the rules for parsing non-negative integers, and if that
is successful, and the value is in the range of the IDL attribute's type, the resulting value must
be returned. If, on the other hand, it fails or returns an out of range value, or if the attribute
is absent, the default value must be returned instead, or −1 if there is no default value.
On setting, if the value is negative, the user agent must throw an
"IndexSizeError" DOMException. Otherwise, the given value
must be converted to the shortest possible string representing the number as a valid
non-negative integer and then that string must be used as the new content attribute
value.
If a reflecting IDL attribute has an unsigned integer type (unsigned long) then, on getting, the content attribute must be
parsed according to the rules for parsing non-negative integers, and if that is
successful, and the value is in the range 0 to 2147483647 inclusive, the resulting value must be
returned. If, on the other hand, it fails or returns an out of range value, or if the attribute is
absent, the default value must be returned instead, or 0 if there is no default value. On setting,
first, if the new value is in the range 0 to 2147483647, then let n be the new value,
otherwise let n be the default value, or 0 if there is no default value; then,
n must be converted to the shortest possible string representing the number as a
valid non-negative integer and that string must be used as the new content attribute
value.
If a reflecting IDL attribute has an unsigned integer type (unsigned long) that is limited to only non-negative numbers
greater than zero, then the behavior is similar to the previous case, but zero is not
allowed. On getting, the content attribute must first be parsed according to the rules for
parsing non-negative integers, and if that is successful, and the value is in the range 1
to 2147483647 inclusive, the resulting value must be returned. If, on the other hand, it fails or
returns an out of range value, or if the attribute is absent, the default value must be returned
instead, or 1 if there is no default value. On setting, if the value is zero, the user agent must
throw an "IndexSizeError" DOMException. Otherwise, first,
if the new value is in the range 1 to 2147483647, then let n be the new value,
otherwise let n be the default value, or 1 if there is no default value; then,
n must be converted to the shortest possible string representing the number as a
valid non-negative integer and that string must be used as the new content attribute
value.
If a reflecting IDL attribute has an unsigned integer type (unsigned long) that is limited to only non-negative numbers
greater than zero with fallback, then the behavior is similar to the previous case, but
disallowed values are converted to the default value. On getting, the content attribute must first
be parsed according to the rules for parsing non-negative integers, and if that is
successful, and the value is in the range 1 to 2147483647 inclusive, the resulting value must be
returned. If, on the other hand, it fails or returns an out of range value, or if the attribute is
absent, the default value must be returned instead. On setting, first, if the new value is in the
range 1 to 2147483647, then let n be the new value, otherwise let n be the
default value; then, n must be converted to the shortest possible string representing
the number as a valid non-negative integer and that string must be used as the new
content attribute value.
If a reflecting IDL attribute has an unsigned integer type (unsigned long) that is clamped to the range
[min, max], then on getting, the content attribute must first be parsed
according to the rules for parsing non-negative integers, and if that is successful,
and the value is between min and max inclusive, the resulting value must be
returned. If it fails, the default value must be returned. If it succeeds but the value is less
than min, min must be returned. If it succeeds but the value is greater than
max, max must be returned. On setting, it behaves the same as setting a
regular reflected unsigned integer.
If a reflecting IDL attribute has a floating-point number type (double or unrestricted
double), then, on getting, the content attribute must be parsed according to the
rules for parsing floating-point number values, and if that is successful, the
resulting value must be returned. If, on the other hand, it fails, or if the attribute is absent,
the default value must be returned instead, or 0.0 if there is no default value. On setting, the
given value must be converted to the best representation of the number as a floating-point
number and then that string must be used as the new content attribute value.
If a reflecting IDL attribute has a floating-point number type (double or unrestricted
double) that is limited to numbers greater than zero, then the behavior is
similar to the previous case, but zero and negative values are not allowed. On getting, the
content attribute must be parsed according to the rules for parsing floating-point number
values, and if that is successful and the value is greater than 0.0, the resulting value
must be returned. If, on the other hand, it fails or returns an out of range value, or if the
attribute is absent, the default value must be returned instead, or 0.0 if there is no default
value. On setting, if the value is less than or equal to zero, then the value must be ignored.
Otherwise, the given value must be converted to the best representation of the number as a
floating-point number and then that string must be used as the new content attribute
value.
The values Infinity and Not-a-Number (NaN) values throw an exception on setting, as defined in Web IDL. [WEBIDL]
If a reflecting IDL attribute has the type DOMTokenList, then on getting it must
return a DOMTokenList object whose associated element is the element in question and
whose associated attribute's local name is the name of the attribute in question.
The HTMLFormControlsCollection and HTMLOptionsCollection interfaces
are collections derived from the
HTMLCollection interface. The HTMLAllCollection interface is a collection, but is not so derived.
HTMLAllCollection interfaceThe HTMLAllCollection interface is used for the legacy document.all attribute. It operates similarly to
HTMLCollection; the main differences are that it allows a staggering variety of
different (ab)uses of its methods to all end up returning something, and that it can be called as
a function as an alternative to property access.
All HTMLAllCollection objects are rooted at a Document
and have a filter that matches all elements, so the elements represented by the
collection of an HTMLAllCollection object consist of all the descendant
elements of the root Document.
Objects that implement the HTMLAllCollection interface are legacy platform objects with an additonal [[Call]] internal
method described in the section below. They also have an
[[IsHTMLDDA]] internal slot.
Objects that implement the HTMLAllCollection interface have several unusual
behaviors, due of the fact that they have an [[IsHTMLDDA]] internal slot:
The ToBoolean abstract operation in JavaScript returns
false when given objects implementing the HTMLAllCollection interface.
The Abstract Equality Comparison algorithm,
when given objects implementing the HTMLAllCollection interface, returns true when
compared to the undefined and null values.
(Comparisons using the Strict Equality Comparison
algorithm, and Abstract Equality comparisons to other values such as strings or objects, are
unaffected.)
The typeof operator in JavaScript returns the string
"undefined" when applied to objects implementing the
HTMLAllCollection interface.
These special behaviors are motivated by a desire for compatibility with two classes of legacy
content: one that uses the presence of document.all as a
way to detect legacy user agents, and one that only supports those legacy user agents and uses
the document.all object without testing for its presence
first. [JAVASCRIPT]
[Exposed =Window ,
LegacyUnenumerableNamedProperties ]
interface HTMLAllCollection {
readonly attribute unsigned long length ;
getter Element (unsigned long index );
getter (HTMLCollection or Element )? namedItem (DOMString name );
(HTMLCollection or Element )? item (optional DOMString nameOrIndex );
// Note: HTMLAllCollection objects have a custom [[Call]] internal method and an [[IsHTMLDDA]] internal slot.
};lengthReturns the number of elements in the collection.
item(index)Returns the item with index index from the collection (determined by tree order).
item(name)item(name)namedItem(name)namedItem(name)Returns the item with ID or name name from the collection.
If there are multiple matching items, then an HTMLCollection object containing all those elements is returned.
Only button, form, iframe,
input, map, meta, object,
select, and textarea elements can have a name for the purpose of this
method; their name is given by the value of their name attribute.
The object's supported property indices are as defined for
HTMLCollection objects.
The supported property names consist of the non-empty values of all the id attributes of all the elements represented by the
collection, and the non-empty values of all the name attributes of
all the "all"-named elements represented by the collection, in
tree order, ignoring later duplicates, with the id of
an element preceding its name if it contributes both, they differ from each
other, and neither is the duplicate of an earlier entry.
On getting, the length
attribute must return the number of nodes represented by the collection.
The indexed property getter must return the result of getting the "all"-indexed element from this
HTMLAllCollection given the passed index.
The namedItem(name)
method must return the result of getting the "all"-named
element(s) from this HTMLAllCollection given name.
The item(nameOrIndex)
method must perform the following steps:
If nameOrIndex was not provided, return null.
Return the result of getting the
"all"-indexed or named element(s) from this HTMLAllCollection, given
nameOrIndex.
The following elements are "all"-named elements:
a,
button,
embed,
form,
frame,
frameset,
iframe,
img,
input,
map,
meta,
object,
select, and
textarea
To get the "all"-indexed element from an
HTMLAllCollection collection given an index index, return the
indexth element in collection, or null if there is no such
indexth element.
To get the "all"-named element(s) from an
HTMLAllCollection collection given a name name, perform the
following steps:
If name is the empty string, return null.
Let subCollection be an HTMLCollection object rooted at the same
Document as collection, whose filter matches only elements that are
either:
"all"-named elements with a name attribute equal to
name, or,
elements with an ID equal to name.
If there is exactly one element in subCollection, then return that element.
Otherwise, if subCollection is empty, return null.
Otherwise, return subCollection.
To get the "all"-indexed or named
element(s) from an HTMLAllCollection collection given
nameOrIndex:
If nameOrIndex, converted to a
JavaScript String value, is an array index property name, return the result of getting the "all"-indexed element from this
HTMLAllCollection given the number represented by nameOrIndex.
Return the result of getting the "all"-named
element(s) from this HTMLAllCollection given
nameOrIndex.
If argumentsList's size is zero, or if argumentsList[0] is undefined, return null.
Let nameOrIndex be the result of converting argumentsList[0] to a DOMString.
Let result be the result of getting the "all"-indexed or named element(s)
from this HTMLAllCollection given nameOrIndex.
Return the result of converting result to an ECMAScript value.
The thisArgument is ignored, and thus code such as Function.prototype.call.call(document.all, null, "x") will still search for
elements. (document.all.call does not exist, since document.all does not inherit from Function.prototype.)
HTMLFormControlsCollection interfaceThe HTMLFormControlsCollection interface is used for
collections of listed
elements in form elements.
[Exposed =Window ]
interface HTMLFormControlsCollection : HTMLCollection {
// inherits length and item()
getter (RadioNodeList or Element )? namedItem (DOMString name ); // shadows inherited namedItem()
};
[Exposed =Window ]
interface RadioNodeList : NodeList {
attribute DOMString value ;
};lengthReturns the number of elements in the collection.
item(index)Returns the item with index index from the collection. The items are sorted in tree order.
namedItem(name)namedItem(name)Returns the item with ID or name name from the collection.
If there are multiple matching items, then a RadioNodeList object containing all those elements is returned.
Returns the value of the first checked radio button represented by the object.
Can be set, to check the first radio button with the given value represented by the object.
The object's supported property indices are as defined for
HTMLCollection objects.
The supported property names consist of the non-empty values of all the id and name attributes of all the
elements represented by the collection, in tree order, ignoring later
duplicates, with the id of an element preceding its name if it contributes both, they differ from each other, and neither is the
duplicate of an earlier entry.
The namedItem(name) method must act according to the following algorithm:
id attribute or a name
attribute equal to name, then return that node and stop the algorithm.id attribute or a name attribute equal
to name, then return null and stop the algorithm.RadioNodeList object representing a live
view of the HTMLFormControlsCollection object, further filtered so that the only
nodes in the RadioNodeList object are those that have either an id attribute or a name attribute equal
to name. The nodes in the RadioNodeList object must be sorted in
tree order.RadioNodeList object.Members of the RadioNodeList interface inherited from the NodeList
interface must behave as they would on a NodeList object.
The value IDL attribute on the
RadioNodeList object, on getting, must return the value returned by running the
following steps:
Let element be the first element in tree order
represented by the RadioNodeList object that is an input element whose
type attribute is in the Radio Button state and whose checkedness is true. Otherwise, let it be null.
If element is null, return the empty string.
If element is an element with no value attribute, return the string "on".
Otherwise, return the value of element's value attribute.
On setting, the value IDL attribute must run the
following steps:
If the new value is the string "on": let element be the first element in tree order
represented by the RadioNodeList object that is an input element whose
type attribute is in the Radio Button state and whose value content attribute is either absent, or present and equal to the new value, if any. If no such element exists, then instead let element be null.
Otherwise: let element be the first element in tree order
represented by the RadioNodeList object that is an input element whose
type attribute is in the Radio Button state and whose value content attribute is present and equal to the new value, if
any. If no such element exists, then instead let element be null.
If element is not null, then set its checkedness to true.
HTMLOptionsCollection interfaceThe HTMLOptionsCollection interface is used for collections of option elements. It is always
rooted on a select element and has attributes and methods that manipulate that
element's descendants.
[Exposed =Window ]
interface HTMLOptionsCollection : HTMLCollection {
// inherits item(), namedItem()
[CEReactions ] attribute unsigned long length ; // shadows inherited length
[CEReactions ] setter void (unsigned long index , HTMLOptionElement ? option );
[CEReactions ] void add ((HTMLOptionElement or HTMLOptGroupElement ) element , optional (HTMLElement or long )? before = null );
[CEReactions ] void remove (long index );
attribute long selectedIndex ;
};length [ = value ]Returns the number of elements in the collection.
When set to a smaller number, truncates the number of option elements in the corresponding container.
When set to a greater number, adds new blank option elements to that container.
item(index)Returns the item with index index from the collection. The items are sorted in tree order.
When index is a greater number than the number of items in the collection, adds
new blank option elements in the corresponding container.
When set to null, removes the item at index index from the collection.
When set to an option element, adds or replaces it at index index
from the collection.
namedItem(name)Returns the item with ID or name name from the collection.
If there are multiple matching items, then the first is returned.
add(element [, before ] )Inserts element before the node given by before.
The before argument can be a number, in which case element is inserted before the item with that number, or an element from the collection, in which case element is inserted before that element.
If before is omitted, null, or a number out of range, then element will be added at the end of the list.
This method will throw a "HierarchyRequestError" DOMException if
element is an ancestor of the element into which it is to be inserted.
remove(index)Removes the item with index index from the collection.
selectedIndex [ = value ]Returns the index of the first selected item, if any, or −1 if there is no selected item.
Can be set, to change the selection.
The object's supported property indices are as defined for
HTMLCollection objects.
On getting, the length
attribute must return the number of nodes represented by the collection.
On setting, the behavior depends on whether the new value is equal to, greater than, or less
than the number of nodes represented by the collection at that time. If the number is
the same, then setting the attribute must do nothing. If the new value is greater, then n new option elements with no attributes and no child nodes must be
appended to the select element on which the HTMLOptionsCollection is
rooted, where n is the difference between the two numbers (new value minus old
value). Mutation events must be fired as if a DocumentFragment containing the new
option elements had been inserted. If the new value is lower, then the last n nodes in the collection must be removed from their parent nodes, where n is the difference between the two numbers (old value minus new value).
Setting length never removes
or adds any optgroup elements, and never adds new children to existing
optgroup elements (though it can remove children from them).
The supported property names consist of the non-empty values of all the id and name attributes of all the
elements represented by the collection, in tree order, ignoring later
duplicates, with the id of an element preceding its name if it contributes both, they differ from each other, and neither is
the duplicate of an earlier entry.
When the user agent is to set the value of a new indexed property or set the value of an existing indexed property for a given property index index to a new value value, it must run the following algorithm:
If value is null, invoke the steps for the remove method with index as
the argument, and return.
Let length be the number of nodes represented by the collection.
Let n be index minus length.
If n is greater than zero, then append a DocumentFragment consisting of n-1 new option elements with no attributes and
no child nodes to the select element on which the HTMLOptionsCollection
is rooted.
If n is greater than or equal to zero, append value to the select
element. Otherwise, replace the indexth element in the collection by value.
The add(element, before) method must act according to the following algorithm:
If element is an ancestor of the select element on which
the HTMLOptionsCollection is rooted, then throw a
"HierarchyRequestError" DOMException.
If before is an element, but that element isn't a descendant of the
select element on which the HTMLOptionsCollection is rooted, then throw
a "NotFoundError" DOMException.
If element and before are the same element, then return.
If before is a node, then let reference be that node. Otherwise, if before is an integer, and there is a beforeth node in the collection, let reference be that node. Otherwise, let reference be null.
If reference is not null, let parent be the parent
node of reference. Otherwise, let parent be the
select element on which the HTMLOptionsCollection is rooted.
Pre-insert element into parent node before reference.
The remove(index) method must act according to the following algorithm:
If the number of nodes represented by the collection is zero, return.
If index is not a number greater than or equal to 0 and less than the number of nodes represented by the collection, return.
Let element be the indexth element in the collection.
Remove element from its parent node.
The selectedIndex IDL
attribute must act like the identically named attribute on the select element on
which the HTMLOptionsCollection is rooted
DOMStringList interfaceThe DOMStringList interface is a non-fashionable retro way of representing a list
of strings.
[Exposed =(Window ,Worker )]
interface DOMStringList {
readonly attribute unsigned long length ;
getter DOMString ? item (unsigned long index );
boolean contains (DOMString string );
};New APIs must use sequence<DOMString> or
equivalent rather than DOMStringList.
lengthReturns the number of strings in strings.
item(index)Returns the string with index index from strings.
contains(string)Returns true if strings contains string, and false otherwise.
Each DOMStringList object has an associated list.
The supported property indices for a DOMStringList object are the
numbers zero to the associated list's size minus one. If its
associated list is empty, it has no supported property
indices.
The length attribute's getter must
return this DOMStringList object's associated list's size.
The item(index) method, when
invoked, must return the indexth item in this DOMStringList object's
associated list, or null if index plus one is greater than this DOMStringList
object's associated list's size.
The contains(string)
method, when invoked, must return true if this DOMStringList object's associated list
contains string, and false otherwise.
This section uses the terminology and typographic conventions from the JavaScript specification. [JAVASCRIPT]
Serializable objects support being serialized, and later deserialized, in a way that is independent of any given JavaScript Realm. This allows them to be stored on disk and later restored, or cloned across agent and even agent cluster boundaries.
Not all objects are serializable objects, and not all aspects of objects that are serializable objects are necessarily preserved when they are serialized.
Platform objects can be serializable objects
if they implement only interfaces decorated with the [Serializable] IDL extended attribute. Such
interfaces must also define the following algorithms:
A set of steps that serializes the data in value into fields of serialized. The resulting data serialized into serialized must be independent of any JavaScript Realm.
These steps may throw an exception if serialization is not possible.
These steps may perform a sub-serialization to serialize nested data structures. They should not call StructuredSerialize directly, as doing so will omit the important memory argument.
The introduction of these steps should omit mention of the forStorage argument if it is not relevant to the algorithm.
A set of steps that deserializes the data in serialized, using it to set up value as appropriate. value will be a newly-created instance of the platform object type in question, with none of its internal data set up; setting that up is the job of these steps.
These steps may throw an exception if deserialization is not possible.
These steps may perform a sub-deserialization to deserialize nested data structures. They should not call StructuredDeserialize directly, as doing so will omit the important targetRealm and memory arguments.
It is up to the definition of individual platform objects to determine what data is serialized and deserialized by these steps. Typically the steps are very symmetric.
The [Serializable] extended attribute must take no
arguments, and must not appear on anything other than an interface. It must appear only once on an
interface. It must not be used on a callback interface. If it appears on a partial interface or an
interface that is really a mixin, then it must also appear on the original or mixed-in-to
interface, and any supplied serialization steps and deserialization
steps for the partial interface or mixin should be understood as being appended to those of
the original or mixed-in-to interface.
Let's say we were defining a platform object Person, which had
associated with it two pieces of associated data:
Person instance or
nullWe could then define Person instances to be serializable
objects by annotating the Person interface with the [Serializable] extended attribute, and defining the
following accompanying algorithms:
Set serialized.[[Name]] to value's associated name value.
Let serializedBestFriend be the sub-serialization of value's associated best friend value.
Set serialized.[[BestFriend]] to serializedBestFriend.
Set value's associated name value to serialized.[[Name]].
Let deserializedBestFriend be the sub-deserialization of serialized.[[BestFriend]].
Set value's associated best friend value to deserializedBestFriend.
Objects defined in the JavaScript specification are handled by the StructuredSerialize abstract operation directly.
Originally, this specification defined the concept of "cloneable objects", which could be cloned from one JavaScript Realm to another. However, to better specify the behavior of certain more complex situations, the model was updated to make the serialization and deserialization explicit.
Transferable objects support being transferred across agents. Transferring is effectively recreating the object while sharing a reference to the underlying data and then detaching the object being transferred. This is useful to transfer ownership of expensive resources. Not all objects are transferable objects and not all aspects of objects that are transferable objects are necessarily preserved when transferred.
Transferring is an irreversible and non-idempotent operation. Once an object has been transferred, it cannot be transferred, or indeed used, again.
Platform objects can be transferable objects
if they implement only interfaces decorated with the [Transferable] IDL extended attribute. Such
interfaces must also define the following algorithms:
A set of steps that transfers the data in value into fields of dataHolder. The resulting data held in dataHolder must be independent of any JavaScript Realm.
These steps may throw an exception if transferral is not possible.
A set of steps that receives the data in dataHolder, using it to set up value as appropriate. value will be a newly-created instance of the platform object type in question, with none of its internal data set up; setting that up is the job of these steps.
These steps may throw an exception if it is not possible to receive the transfer.
It is up to the definition of individual platform objects to determine what data is transferred by these steps. Typically the steps are very symmetric.
The [Transferable] extended attribute must take no
arguments, and must not appear on anything other than an interface. It must appear only once on an
interface. It must not be used on a callback interface. If it appears on a partial interface or an
interface that is really a mixin, then it must also appear on the original or mixed-in-to
interface, and any supplied transfer steps and transfer-receiving
steps for the partial interface or mixin should be understood as being appended to those of
the original or mixed-in-to interface.
Platform objects that are transferable objects have a [[Detached]] internal slot. This is used to ensure that once a platform object has been transferred, it cannot be transferred again.
Objects defined in the JavaScript specification are handled by the StructuredSerializeWithTransfer abstract operation directly.
The StructuredSerializeInternal abstract operation takes as input a JavaScript value value and serializes it to a Realm-independent form, represented here as a Record. This serialized form has all the information necessary to later deserialize into a new JavaScript value in a different Realm.
This process can throw an exception, for example when trying to serialize un-serializable objects.
If memory was not supplied, let memory be an empty map.
The purpose of the memory map is to avoid serializing objects twice. This ends up preserving cycles and the identity of duplicate objects in graphs.
If memory[value] exists, then return memory[value].
Let deep be false.
If Type(value) is Undefined, Null, Boolean, Number, BigInt, or String, then return { [[Type]]: "primitive", [[Value]]: value }. [JSBIGINT]
If Type(value) is Symbol, then throw a
"DataCloneError" DOMException.
Let serialized be an uninitialized value.
If value has a [[BooleanData]] internal slot, then set serialized to { [[Type]]: "Boolean", [[BooleanData]]: value.[[BooleanData]] }.
Otherwise, if value has a [[NumberData]] internal slot, then set serialized to { [[Type]]: "Number", [[NumberData]]: value.[[NumberData]] }.
Otherwise, if value has a [[BigIntData]] internal slot, then set serialized to { [[Type]]: "BigInt", [[BigIntData]]: value.[[BigIntData]] }. [JSBIGINT]
Otherwise, if value has a [[StringData]] internal slot, then set serialized to { [[Type]]: "String", [[StringData]]: value.[[StringData]] }.
Otherwise, if value has a [[DateValue]] internal slot, then set serialized to { [[Type]]: "Date", [[DateValue]]: value.[[DateValue]] }.
Otherwise, if value has a [[RegExpMatcher]] internal slot, then set serialized to { [[Type]]: "RegExp", [[RegExpMatcher]]: value.[[RegExpMatcher]], [[OriginalSource]]: value.[[OriginalSource]], [[OriginalFlags]]: value.[[OriginalFlags]] }.
Otherwise, if value has an [[ArrayBufferData]] internal slot, then:
Let size be value.[[ArrayBufferByteLength]].
If ! IsSharedArrayBuffer(value) is true, then:
If forStorage is true, then throw a
"DataCloneError" DOMException.
Set serialized to { [[Type]]: "SharedArrayBuffer", [[ArrayBufferData]]: value.[[ArrayBufferData]], [[ArrayBufferByteLength]]: size, [[AgentCluster]]: the current Realm Record's corresponding agent cluster }.
Otherwise:
If ! IsDetachedBuffer(value) is true, then throw a
"DataCloneError" DOMException.
Let dataCopy be ? CreateByteDataBlock(size).
This can throw a RangeError exception
upon allocation failure.
Perform ! CopyDataBlockBytes(dataCopy, 0, value.[[ArrayBufferData]], 0, size).
Set serialized to { [[Type]]: "ArrayBuffer", [[ArrayBufferData]]: dataCopy, [[ArrayBufferByteLength]]: size }.
Otherwise, if value has a [[ViewedArrayBuffer]] internal slot, then:
Let buffer be the value of value's [[ViewedArrayBuffer]] internal slot.
Let bufferSerialized be ? StructuredSerializeInternal(buffer, forStorage, memory).
Assert: bufferSerialized.[[Type]] is "ArrayBuffer".
If value has a [[DataView]] internal slot, then set serialized to { [[Type]]: "ArrayBufferView", [[Constructor]]: "DataView", [[ArrayBufferSerialized]]: bufferSerialized, [[ByteLength]]: value.[[ByteLength]], [[ByteOffset]]: value.[[ByteOffset]] }.
Otherwise:
Assert: value has a [[TypedArrayName]] internal slot.
Set serialized to { [[Type]]: "ArrayBufferView", [[Constructor]]: value.[[TypedArrayName]], [[ArrayBufferSerialized]]: bufferSerialized, [[ByteLength]]: value.[[ByteLength]], [[ByteOffset]]: value.[[ByteOffset]], [[ArrayLength]]: value.[[ArrayLength]] }.
Otherwise, if value has [[MapData]] internal slot, then:
Set serialized to { [[Type]]: "Map", [[MapData]]: a new empty List }.
Set deep to true.
Otherwise, if value has [[SetData]] internal slot, then:
Set serialized to { [[Type]]: "Set", [[SetData]]: a new empty List }.
Set deep to true.
Otherwise, if value has an [[ErrorData]] internal slot and value is not a platform object, then:
Let prototype be "Error".
Let valueProto be ! value.[[GetPrototypeOf]]().
If valueProto is %EvalErrorPrototype%, then set prototype to "EvalError".
If valueProto is %RangeErrorPrototype%, then set prototype to "RangeError".
If valueProto is %ReferenceErrorPrototype%, then set prototype to "ReferenceError".
If valueProto is %SyntaxErrorPrototype%, then set prototype to "SyntaxError".
If valueProto is %TypeErrorPrototype%, then set prototype to "TypeError".
If valueProto is %URIErrorPrototype%, then set prototype to "URIError".
Let valueMessageDesc be ? value.[[GetOwnProperty]]("message").
Let message be undefined if IsDataDescriptor(valueMessageDesc) is false, and ? ToString(valueMessageDesc.[[Value]]) otherwise.
Set serialized to { [[Type]]: "Error", [[Prototype]]: prototype, [[Message]]: message }.
User agents should attach a serialized representation of any interesting accompanying
data which are not yet specified, notably the stack property, to
serialized.
See the Error Stacks proposal for in-progress work on specifying this data. [JSERRORSTACKS]
Otherwise, if value is an Array exotic object, then:
Let valueLenDescriptor be ?
OrdinaryGetOwnProperty(value, "length").
Let valueLen be valueLenDescriptor.[[Value]].
Set serialized to { [[Type]]: "Array", [[Length]]: valueLen, [[Properties]]: a new empty List }.
Set deep to true.
Otherwise, if value is a platform object that is a serializable object:
If value has a [[Detached]] internal slot whose value is true,
then throw a "DataCloneError" DOMException.
Let typeString be the identifier of the primary interface of value.
Set serialized to { [[Type]]: typeString }.
Set deep to true.
Otherwise, if value is a platform object, then throw a
"DataCloneError" DOMException.
Otherwise, if IsCallable(value) is true, then throw a
"DataCloneError" DOMException.
Otherwise, if value has any internal slot other than [[Prototype]] or
[[Extensible]], then throw a "DataCloneError"
DOMException.
For instance, a [[PromiseState]] or [[WeakMapData]] internal slot.
Otherwise, if value is an exotic object, then throw a
"DataCloneError" DOMException.
For instance, a proxy object.
Otherwise:
Set serialized to { [[Type]]: "Object", [[Properties]]: a new empty List }.
Set deep to true.
Set memory[value] to serialized.
If deep is true, then:
If value has a [[MapData]] internal slot, then:
Let copiedList be a new empty List.
For each Record { [[Key]], [[Value]] } entry of value.[[MapData]]:
For each Record { [[Key]], [[Value]] } entry of copiedList:
Let serializedKey be ? StructuredSerializeInternal(entry.[[Key]], forStorage, memory).
Let serializedValue be ? StructuredSerializeInternal(entry.[[Value]], forStorage, memory).
Append { [[Key]]: serializedKey, [[Value]]: serializedValue } to serialized.[[MapData]].
Otherwise, if value has a [[SetData]] internal slot, then:
Let copiedList be a new empty List.
For each entry of value.[[SetData]]:
If entry is not the special value empty, append entry to copiedList.
For each entry of copiedList:
Let serializedEntry be ? StructuredSerializeInternal(entry, forStorage, memory).
Append serializedEntry to serialized.[[SetData]].
Otherwise, if value is a platform object that is a serializable object, then perform the appropriate serialization steps given value, serialized, and forStorage.
The serialization steps may need to perform a sub-serialization. This is an operation which takes as input a value subValue, and returns StructuredSerializeInternal(subValue, forStorage, memory). (In other words, a sub-serialization is a specialization of StructuredSerializeInternal to be consistent within this invocation.)
Otherwise:
Let enumerableKeys be a new empty List.
For each key in ! value.[[OwnPropertyKeys]]():
For each key in enumerableKeys:
If ! HasOwnProperty(value, key) is true, then:
Let inputValue be ? value.[[Get]](key, value).
Let outputValue be ? StructuredSerializeInternal(inputValue, forStorage, memory).
Append { [[Key]]: key, [[Value]]: outputValue } to serialized.[[Properties]].
The key collection performed above is very similar to the JavaScript specification's EnumerableOwnProperties operation, but crucially it uses the deterministic ordering provided by the [[OwnPropertyKeys]] internal method, instead of reordering the keys in an unspecified manner as EnumerableOwnProperties does. [JAVASCRIPT]
Return serialized.
It's important to realize that the Records produced by StructuredSerializeInternal might contain "pointers" to other records that create circular references. For example, when we pass the following JavaScript object into StructuredSerializeInternal:
const o = {};
o. myself = o; it produces the following result:
{
[[Type]]: "Object",
[[Properties]]: «
{
[[Key]]: "myself",
[[Value]]: <a pointer to this whole structure>
}
»
}
Return ? StructuredSerializeInternal(value, false).
Return ? StructuredSerializeInternal(value, true).
The StructuredDeserialize abstract operation takes as input a Record serialized, which was previously produced by StructuredSerialize or StructuredSerializeForStorage, and deserializes it into a new JavaScript value, created in targetRealm.
This process can throw an exception, for example when trying to allocate memory for the new
objects (especially ArrayBuffer objects).
If memory was not supplied, let memory be an empty map.
The purpose of the memory map is to avoid deserializing objects twice. This ends up preserving cycles and the identity of duplicate objects in graphs.
If memory[serialized] exists, then return memory[serialized].
Let deep be false.
Let value be an uninitialized value.
If serialized.[[Type]] is "primitive", then set value to serialized.[[Value]].
Otherwise, if serialized.[[Type]] is "Boolean", then set value to a new Boolean object in targetRealm whose [[BooleanData]] internal slot value is serialized.[[BooleanData]].
Otherwise, if serialized.[[Type]] is "Number", then set value to a new Number object in targetRealm whose [[NumberData]] internal slot value is serialized.[[NumberData]].
Otherwise, if serialized.[[Type]] is "BigInt", then set value to a new BigInt object in targetRealm whose [[BigIntData]] internal slot value is serialized.[[BigIntData]]. [JSBIGINT]
Otherwise, if serialized.[[Type]] is "String", then set value to a new String object in targetRealm whose [[StringData]] internal slot value is serialized.[[StringData]].
Otherwise, if serialized.[[Type]] is "Date", then set value to a new Date object in targetRealm whose [[DateValue]] internal slot value is serialized.[[DateValue]].
Otherwise, if serialized.[[Type]] is "RegExp", then set value to a new RegExp object in targetRealm whose [[RegExpMatcher]] internal slot value is serialized.[[RegExpMatcher]], whose [[OriginalSource]] internal slot value is serialized.[[OriginalSource]], and whose [[OriginalFlags]] internal slot value is serialized.[[OriginalFlags]].
Otherwise, if serialized.[[Type]] is "SharedArrayBuffer", then:
If targetRealm's corresponding agent cluster is not
serialized.[[AgentCluster]], then then throw a
"DataCloneError" DOMException.
Otherwise, set value to a new SharedArrayBuffer object in targetRealm whose [[ArrayBufferData]] internal slot value is serialized.[[ArrayBufferData]] and whose [[ArrayBufferByteLength]] internal slot value is serialized.[[ArrayBufferByteLength]].
Otherwise, if serialized.[[Type]] is "ArrayBuffer", then set value to a new ArrayBuffer object in targetRealm whose [[ArrayBufferData]] internal slot value is serialized.[[ArrayBufferData]], and whose [[ArrayBufferByteLength]] internal slot value is serialized.[[ArrayBufferByteLength]].
If this throws an exception, catch it, and then throw a
"DataCloneError" DOMException.
This step might throw an exception if there is not enough memory available to create such an ArrayBuffer object.
Otherwise, if serialized.[[Type]] is "ArrayBufferView", then:
Let deserializedArrayBuffer be ? StructuredDeserialize(serialized.[[ArrayBufferSerialized]], targetRealm, memory).
If serialized.[[Constructor]] is "DataView", then set value to a new DataView object in targetRealm whose [[ViewedArrayBuffer]] internal slot value is deserializedArrayBuffer, whose [[ByteLength]] internal slot value is serialized.[[ByteLength]], and whose [[ByteOffset]] internal slot value is serialized.[[ByteOffset]].
Otherwise, set value to a new typed array object in targetRealm, using the constructor given by serialized.[[Constructor]], whose [[ViewedArrayBuffer]] internal slot value is deserializedArrayBuffer, whose [[TypedArrayName]] internal slot value is serialized.[[Constructor]], whose [[ByteLength]] internal slot value is serialized.[[ByteLength]], whose [[ByteOffset]] internal slot value is serialized.[[ByteOffset]], and whose [[ArrayLength]] internal slot value is serialized.[[ArrayLength]].
Otherwise, if serialized.[[Type]] is "Map", then:
Set value to a new Map object in targetRealm whose [[MapData]] internal slot value is a new empty List.
Set deep to true.
Otherwise, if serialized.[[Type]] is "Set", then:
Set value to a new Set object in targetRealm whose [[SetData]] internal slot value is a new empty List.
Set deep to true.
Otherwise, if serialized.[[Type]] is "Array", then:
Let outputProto be targetRealm.[[Intrinsics]].[[%ArrayPrototype%]].
Set value to ! ArrayCreate(serialized.[[Length]], outputProto).
Set deep to true.
Otherwise, if serialized.[[Type]] is "Object", then:
Set value to a new Object in targetRealm.
Set deep to true.
Otherwise, if serialized.[[Type]] is "Error", then:
Let prototype be %ErrorPrototype%.
If serialized.[[Prototype]] is "EvalError", then set prototype to %EvalErrorPrototype%.
If serialized.[[Prototype]] is "RangeError", then set prototype to %RangeErrorPrototype%.
If serialized.[[Prototype]] is "ReferenceError", then set prototype to %ReferenceErrorPrototype%.
If serialized.[[Prototype]] is "SyntaxError", then set prototype to %SyntaxErrorPrototype%.
If serialized.[[Prototype]] is "TypeError", then set prototype to %TypeErrorPrototype%.
If serialized.[[Prototype]] is "URIError", then set prototype to %URIErrorPrototype%.
Let message be serialized.[[Message]].
Set value to ! ObjectCreate(prototype, « [[ErrorData]] »).
Let messageDesc be PropertyDescriptor{ [[Value]]: message, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true }.
If message is not undefined, then perform !
OrdinaryDefineOwnProperty(value, "message",
messageDesc).
Any interesting accompanying data attached to serialized should be deserialized and attached to value.
Otherwise:
Let interfaceName be serialized.[[Type]].
If the interface identified by interfaceName is not
exposed in targetRealm, then throw a
"DataCloneError" DOMException.
Set value to a new instance of the interface identified by interfaceName, created in targetRealm.
Set deep to true.
Set memory[serialized] to value.
If deep is true, then:
If serialized.[[Type]] is "Map", then:
For each Record { [[Key]], [[Value]] } entry of serialized.[[MapData]]:
Let deserializedKey be ? StructuredDeserialize(entry.[[Key]], targetRealm, memory).
Let deserializedValue be ? StructuredDeserialize(entry.[[Value]], targetRealm, memory).
Append { [[Key]]: deserializedKey, [[Value]]: deserializedValue } to value.[[MapData]].
Otherwise, if serialized.[[Type]] is "Set", then:
For each entry of serialized.[[SetData]]:
Let deserializedEntry be ? StructuredDeserialize(entry, targetRealm, memory).
Append deserializedEntry to value.[[SetData]].
Otherwise, if serialized.[[Type]] is "Array" or "Object", then:
For each Record { [[Key]], [[Value]] } entry of serialized.[[Properties]]:
Let deserializedValue be ? StructuredDeserialize(entry.[[Value]], targetRealm, memory).
Let result be ! CreateDataProperty(value, entry.[[Key]], deserializedValue).
Assert: result is true.
Otherwise:
Perform the appropriate deserialization steps for the interface identified by serialized.[[Type]], given serialized and value.
The deserialization steps may need to perform a sub-deserialization. This is an operation which takes as input a previously-serialized Record subSerialized, and returns StructuredDeserialize(subSerialized, targetRealm, memory). (In other words, a sub-deserialization is a specialization of StructuredDeserialize to be consistent within this invocation.)
Return value.
Let memory be an empty map.
In addition to how it is used normally by StructuredSerializeInternal, in this algorithm memory is also used to ensure that StructuredSerializeInternal ignores items in transferList, and let us do our own handling instead.
For each transferable of transferList:
If transferable has neither an [[ArrayBufferData]] internal slot nor a
[[Detached]] internal slot, then throw a
"DataCloneError" DOMException.
If transferable has an [[ArrayBufferData]] internal slot and !
IsSharedArrayBuffer(transferable) is true, then throw a
"DataCloneError" DOMException.
If memory[transferable] exists,
then throw a "DataCloneError" DOMException.
Set memory[transferable] to { [[Type]]: an uninitialized value }.
transferable is not transferred yet as transferring has side effects and StructuredSerializeInternal needs to be able to throw first.
Let serialized be ? StructuredSerializeInternal(value, false, memory).
Let transferDataHolders be a new empty List.
For each transferable of transferList:
If transferable has an [[ArrayBufferData]] internal slot and !
IsDetachedBuffer(transferable) is true, then throw a
"DataCloneError" DOMException.
If transferable has a [[Detached]] internal slot and
transferable.[[Detached]] is true, then throw a
"DataCloneError" DOMException.
Let dataHolder be memory[transferable].
If transferable has an [[ArrayBufferData]] internal slot, then:
Set dataHolder.[[Type]] to "ArrayBuffer".
Set dataHolder.[[ArrayBufferData]] to transferable.[[ArrayBufferData]].
Set dataHolder.[[ArrayBufferByteLength]] to transferable.[[ArrayBufferByteLength]].
Perform ? DetachArrayBuffer(transferable).
Specifications can use the [[ArrayBufferDetachKey]] internal slot to prevent
ArrayBuffers from being detached. This is used in
WebAssembly JavaScript Interface, for example. [WASMJS]
Otherwise:
Assert: transferable is a platform object that is a transferable object.
Let interfaceName be the identifier of the primary interface of transferable.
Set dataHolder.[[Type]] to interfaceName.
Perform the appropriate transfer steps for the interface identified by interfaceName, given transferable and dataHolder.
Set transferable.[[Detached]] to true.
Append dataHolder to transferDataHolders.
Return { [[Serialized]]: serialized, [[TransferDataHolders]]: transferDataHolders }.
Let memory be an empty map.
Analogous to StructuredSerializeWithTransfer, in addition to how it is used normally by StructuredDeserialize, in this algorithm memory is also used to ensure that StructuredDeserialize ignores items in serializeWithTransferResult.[[TransferDataHolders]], and let us do our own handling instead.
Let transferredValues be a new empty List.
For each transferDataHolder of serializeWithTransferResult.[[TransferDataHolders]]:
Let value be an uninitialized value.
If transferDataHolder.[[Type]] is "ArrayBuffer", then set value to a new ArrayBuffer object in targetRealm whose [[ArrayBufferData]] internal slot value is transferDataHolder.[[ArrayBufferData]], and whose [[ArrayBufferByteLength]] internal slot value is transferDataHolder.[[ArrayBufferByteLength]].
In cases where the original memory occupied by [[ArrayBufferData]] is accessible during the deserialization, this step is unlikely to throw an exception, as no new memory needs to be allocated: the memory occupied by [[ArrayBufferData]] is instead just getting transferred into the new ArrayBuffer. This could be true, for example, when both the source and target Realms are in the same process.
Otherwise:
Let interfaceName be transferDataHolder.[[Type]].
If the interface identified by interfaceName is not exposed in
targetRealm, then throw a "DataCloneError"
DOMException.
Set value to a new instance of the interface identified by interfaceName, created in targetRealm.
Perform the appropriate transfer-receiving steps for the interface identified by interfaceName given transferDataHolder and value.
Set memory[transferDataHolder] to value.
Append value to transferredValues.
Let deserialized be ? StructuredDeserialize(serializeWithTransferResult.[[Serialized]], targetRealm, memory).
Return { [[Deserialized]]: deserialized, [[TransferredValues]]: transferredValues }.
Other specifications may use the abstract operations defined here. The following provides some guidance on when each abstract operation is typically useful, with examples.
Cloning a value to another JavaScript Realm, with a transfer list, but where the target Realm is not known ahead of time. In this case the serialization step can be performed immediately, with the deserialization step delayed until the target Realm becomes known.
messagePort.postMessage()
uses this pair of abstract operations, as the destination Realm is not known until the
MessagePort has been shipped.
Creating a JavaScript Realm-independent snapshot of a given value which can be saved for an indefinite amount of time, and then reified back into a JavaScript value later, possibly multiple times.
StructuredSerializeForStorage can be used for situations where the serialization
is anticipated to be stored in a persistent manner, instead of passed between Realms. It throws
when attempting to serialize SharedArrayBuffer objects, since storing shared memory
does not make sense. Similarly, it can throw or possibly have different behavior when given a
platform object with custom serialization steps when the
forStorage argument is true.
history.pushState() and history.replaceState() use
StructuredSerializeForStorage on author-supplied state objects, storing them as
serialized state in the appropriate session history entry. Then,
StructuredDeserialize is used so that the history.state property can return a clone of the
originally-supplied state object.
broadcastChannel.postMessage() uses
StructuredSerialize on its input, then uses StructuredDeserialize
multiple times on the result to produce a fresh clone for each destination being broadcast
to. Note that transferring does not make sense in multi-destination situations.
Any API for persisting JavaScript values to the filesystem would also use StructuredSerializeForStorage on its input and StructuredDeserialize on its output.
In general, call sites may pass in Web IDL values instead of JavaScript values; this is to be understood to perform an implicit conversion to the JavaScript value before invoking these algorithms.
This specification used to define a "structured clone" algorithm, and more recently a StructuredClone abstract operation. However, in practice all known uses of it were better served by separate serialization and deserialization steps, so it was removed.
Call sites that are not invoked as a result of author code synchronously calling into a user agent method must take care to properly prepare to run script and prepare to run a callback before invoking StructuredSerialize, StructuredSerializeForStorage, or StructuredSerializeWithTransfer abstract operations, if they are being performed on arbitrary objects. This is necessary because the serialization process can invoke author-defined accessors as part of its final deep-serialization steps, and these accessors could call into operations that rely on the entry and incumbent concepts being properly set up.
window.postMessage() performs
StructuredSerializeWithTransfer on its arguments, but is careful to do so
immediately, inside the synchronous portion of its algorithm. Thus it is able to use the
algorithms without needing to prepare to run script and prepare to run a
callback.
In contrast, a hypothetical API that used StructuredSerialize to serialize some author-supplied object periodically, directly from a task on the event loop, would need to ensure it performs the appropriate preparations beforehand. As of this time, we know of no such APIs on the platform; usually it is simpler to perform the serialization ahead of time, as a synchronous consequence of author code.
Every XML and HTML document in an HTML UA is represented by a Document object. [DOM]
The Document object's URL is defined in DOM. It is initially set when
the Document object is created, but can change during the lifetime of the
Document object; for example, it changes when the user navigates to a fragment on the page
and when the pushState() method is called with a new
URL. [DOM]
Interactive user agents typically expose the Document object's
URL in their user interface. This is the primary
mechanism by which a user can tell if a site is attempting to impersonate another.
When a Document is created by a script using
the createDocument() or createHTMLDocument() the
Document is both ready for post-load tasks and completely
loaded immediately.
The document's referrer is a string (representing a URL)
that can be set when the Document is created. If it is not explicitly set, then its
value is the empty string.
Document objectDOM defines a Document interface, which
this specification extends significantly.
enum DocumentReadyState { "loading" , "interactive" , "complete" };
typedef (HTMLScriptElement or SVGScriptElement ) HTMLOrSVGScriptElement ;
[OverrideBuiltins ]
partial interface Document {
// resource metadata management
[PutForwards =href , Unforgeable ] readonly attribute Location ? location ;
attribute USVString domain ;
readonly attribute USVString referrer ;
attribute USVString cookie ;
readonly attribute DOMString lastModified ;
readonly attribute DocumentReadyState readyState ;
// DOM tree accessors
getter object (DOMString name );
[CEReactions ] attribute DOMString title ;
[CEReactions ] attribute DOMString dir ;
[CEReactions ] attribute HTMLElement ? body ;
readonly attribute HTMLHeadElement ? head ;
[SameObject ] readonly attribute HTMLCollection images ;
[SameObject ] readonly attribute HTMLCollection embeds ;
[SameObject ] readonly attribute HTMLCollection plugins ;
[SameObject ] readonly attribute HTMLCollection links ;
[SameObject ] readonly attribute HTMLCollection forms ;
[SameObject ] readonly attribute HTMLCollection scripts ;
NodeList getElementsByName (DOMString elementName );
readonly attribute HTMLOrSVGScriptElement ? currentScript ; // classic scripts in a document tree only
// dynamic markup insertion
[CEReactions ] Document open (optional DOMString unused1 , optional DOMString unused2 ); // both arguments are ignored
WindowProxy ? open (USVString url , DOMString name , DOMString features );
[CEReactions ] void close ();
[CEReactions ] void write (DOMString ... text );
[CEReactions ] void writeln (DOMString ... text );
// user interaction
readonly attribute WindowProxy ? defaultView ;
boolean hasFocus ();
[CEReactions ] attribute DOMString designMode ;
[CEReactions ] boolean execCommand (DOMString commandId , optional boolean showUI = false , optional DOMString value = "");
boolean queryCommandEnabled (DOMString commandId );
boolean queryCommandIndeterm (DOMString commandId );
boolean queryCommandState (DOMString commandId );
boolean queryCommandSupported (DOMString commandId );
DOMString queryCommandValue (DOMString commandId );
// special event handler IDL attributes that only apply to Document objects
[LenientThis ] attribute EventHandler onreadystatechange ;
// also has obsolete members
};
Document includes GlobalEventHandlers ;
Document includes DocumentAndElementEventHandlers ;The Document has an HTTPS state (an HTTPS state value), initially "none", which represents the security properties of the network channel used to
deliver the Document's data.
The Document has a referrer policy (a referrer policy), initially the
empty string, which represents the default referrer policy used by fetches initiated by the Document.
The Document has a CSP list, which is a CSP list
containing all of the Content Security Policy objects active for the document. The
list is empty unless otherwise specified.
The Document has a feature policy, which is a feature policy, which is initially empty.
The Document has a module map, which is a module map,
initially empty.
DocumentOrShadowRoot interfaceDOM defines the DocumentOrShadowRoot mixin, which this specification
extends.
partial interface mixin DocumentOrShadowRoot {
readonly attribute Element ? activeElement ;
};referrerReturns the URL of the Document
from which the user navigated to this one, unless it was blocked or there was no such document,
in which case it returns the empty string.
The noreferrer link type can be used to block the
referrer.
The referrer attribute must return
the document's referrer.
cookie [ = value ]Returns the HTTP cookies that apply to the Document. If there are no cookies or
cookies can't be applied to this resource, the empty string will be returned.
Can be set, to add a new cookie to the element's set of HTTP cookies.
If the contents are sandboxed into a
unique origin (e.g. in an iframe with the sandbox attribute), a
"SecurityError" DOMException will be thrown on getting
and setting.
The cookie attribute represents the
cookies of the resource identified by the document's URL.
A Document object that falls into one of the following conditions is a
cookie-averse Document object:
Document object whose browsing
context is null.Document whose URL's scheme is not a network scheme.On getting, if the document is a cookie-averse Document
object, then the user agent must return the empty string. Otherwise, if the
Document's origin is an opaque
origin, the user agent must throw a "SecurityError"
DOMException. Otherwise, the user agent must return the cookie-string
for the document's URL for a "non-HTTP" API, decoded
using UTF-8 decode without BOM. [COOKIES]
On setting, if the document is a cookie-averse Document object, then
the user agent must do nothing. Otherwise, if the Document's origin is
an opaque origin, the user agent must throw a
"SecurityError" DOMException. Otherwise, the user agent
must act as it would when receiving a
set-cookie-string for the document's URL via a
"non-HTTP" API, consisting of the new value encoded as UTF-8.
[COOKIES] [ENCODING]
Since the cookie attribute is accessible
across frames, the path restrictions on cookies are only a tool to help manage which cookies are
sent to which parts of the site, and are not in any way a security feature.
The cookie attribute's getter and
setter synchronously access shared state. Since there is no locking mechanism, other browsing
contexts in a multiprocess user agent can modify cookies while scripts are running. A site could,
for instance, try to read a cookie, increment its value, then write it back out, using the new
value of the cookie as a unique identifier for the session; if the site does this twice in two
different browser windows at the same time, it might end up using the same "unique" identifier for
both sessions, with potentially disastrous effects.
lastModifiedReturns the date of the last modification to the document, as reported by the server, in the
form "MM/DD/YYYY hh:mm:ss", in the user's local time zone.
If the last modification date is not known, the current time is returned instead.
The lastModified attribute, on
getting, must return the date and time of the Document's source file's last
modification, in the user's local time zone, in the following format:
All the numeric components above, other than the year, must be given as two ASCII digits representing the number in base ten, zero-padded if necessary. The year must be given as the shortest possible string of four or more ASCII digits representing the number in base ten, zero-padded if necessary.
The Document's source file's last modification date and time must be derived from
relevant features of the networking protocols used, e.g. from the value of the HTTP `Last-Modified` header of the document, or from metadata in the
file system for local files. If the last modification date and time are not known, the attribute
must return the current date and time in the above format.
readyStateReturns "loading" while the Document is loading, "interactive" once it is finished parsing but still loading subresources, and
"complete" once it has loaded.
The readystatechange event fires on the
Document object when this value changes.
The DOMContentLoaded event fires after the transition to
"interactive" but before the transition to "complete", at the point where all subresources apart from async script elements have loaded.
Each document has a current document readiness. When a Document object
is created, it must have its current document readiness set to the string "loading" if the document is associated with an HTML parser, an
XML parser, or an XSLT processor, and to the string "complete"
otherwise. Various algorithms during page loading affect this value. When the value is set, the
user agent must fire an event named readystatechange at the Document object.
A Document is said to have an active parser if it is associated with an
HTML parser or an XML parser that has not yet been stopped or aborted.
The readyState IDL attribute must, on
getting, return the current document readiness.
The html element of a document is its document element,
if it's an html element, and null otherwise.
headReturns the head element.
The head element of a document is the first head element
that is a child of the html element, if there is one, or null
otherwise.
The head attribute, on getting, must return
the head element of the document (a head element or
null).
Support: documentheadChrome for Android 75+Chrome 4+iOS Safari 4.0+Samsung Internet 4+UC Browser for Android 12.12+Firefox 4+Safari 5.1+IE 9+Edge 12+Opera Mini all+Opera 11+Android Browser 2.3+
Source: caniuse.com
title [ = value ]Returns the document's title, as given by the title element for
HTML and as given by the SVG title element for SVG.
Can be set, to update the document's title. If there is no appropriate element to update, the new value is ignored.
The title element of a document is the first title element
in the document (in tree order), if there is one, or null otherwise.
The title attribute
must, on getting, run the following algorithm:
If the document element is an SVG svg element, then
let value be the child text content of the first SVG
title element that is a child of the document element.
Otherwise, let value be the child text content of the
title element, or the empty string if the title
element is null.
Strip and collapse ASCII whitespace in value.
Return value.
On setting, the steps corresponding to the first matching condition in the following list must be run:
svg elementIf there is an SVG title element that is a child of the
document element, let element be the first such element.
Otherwise:
Let element be the result of creating an
element given the document element's node document, title, and the SVG namespace.
Insert element as the first child of the document element.
String replace all with the given value within element.
If the title element is null and the head
element is null, then return.
If the title element is non-null, let element be
the title element.
Otherwise:
Let element be the result of creating an
element given the document element's node document,
title, and the HTML namespace.
Append element to the
head element.
String replace all with the given value within element.
Do nothing.
body [ = value ]Returns the body element.
Can be set, to replace the body element.
If the new value is not a body or frameset element, this will throw
a "HierarchyRequestError" DOMException.
The body element of a document is the first of the html
element's children that is either a body element or a frameset
element, or null if there is no such element.
The body attribute, on getting, must return
the body element of the document (either a body element, a
frameset element, or null). On setting, the following algorithm must be run:
body or frameset element, then throw a
"HierarchyRequestError" DOMException.HierarchyRequestError" DOMException.The value returned by the body getter is
not always the one passed to the setter.
In this example, the setter successfully inserts a body element (though this is
non-conforming since SVG does not allow a body as child of SVG
svg). However the getter will return null because the document element is not
html.
< svg xmlns = "http://www.w3.org/2000/svg" >
< script >
document. body = document. createElementNS( "http://www.w3.org/1999/xhtml" , "body" );
console. assert( document. body === null );
</ script >
</ svg > imagesReturns an HTMLCollection of the img elements in the Document.
embedspluginsReturn an HTMLCollection of the embed elements in the Document.
linksReturns an HTMLCollection of the a and area elements
in the Document that have href
attributes.
formsReturn an HTMLCollection of the form elements in the Document.
scriptsReturn an HTMLCollection of the script elements in the Document.
The images attribute must return an
HTMLCollection rooted at the Document node, whose filter matches only
img elements.
The embeds attribute must return an
HTMLCollection rooted at the Document node, whose filter matches only
embed elements.
The plugins attribute must return the
same object as that returned by the embeds
attribute.
The links attribute must return an
HTMLCollection rooted at the Document node, whose filter matches only
a elements with href attributes and
area elements with href attributes.
The forms attribute must return an
HTMLCollection rooted at the Document node, whose filter matches only
form elements.
The scripts attribute must return an
HTMLCollection rooted at the Document node, whose filter matches only
script elements.
getElementsByName(name)Returns a NodeList of elements in the Document that have a name attribute with the value name.
The getElementsByName(name) method takes a string name, and must
return a live NodeList containing all the HTML elements in
that document that have a name attribute whose value is equal to the name argument (in a case-sensitive manner), in tree
order. When the method is invoked on a Document object again with the same
argument, the user agent may return the same as the object returned by the earlier call. In other
cases, a new NodeList object must be returned.
currentScriptReturns the script element, or the SVG script element,
that is currently executing, as long as the element represents a classic script.
In the case of reentrant script execution, returns the one that most recently started executing
amongst those that have not yet finished executing.
Returns null if the Document is not currently executing a script
or SVG script element (e.g., because the running script is an event
handler, or a timeout), or if the currently executing script or SVG
script element represents a module script.
The currentScript attribute, on
getting, must return the value to which it was most recently set. When the Document
is created, the currentScript must be
initialized to null.
Support: document-currentscriptChrome for Android 75+Chrome 29+iOS Safari 8+Samsung Internet 4+UC Browser for Android 12.12+Firefox 4+Safari 8+IE NoneEdge 12+Opera Mini NoneOpera 16+Android Browser 4.4+
Source: caniuse.com
This API has fallen out of favor in the implementer and standards community, as
it globally exposes script or SVG script elements. As such,
it is not available in newer contexts, such as when running module
scripts or when running scripts in a shadow tree. We are looking into creating
a new solution for identifying the running script in such contexts, which does not make it
globally available: see issue #1013.
The Document interface supports named properties. The supported property names of a
Document object document at any moment consist of the following, in
tree order according to the element that contributed them, ignoring later duplicates,
and with values from id attributes coming before values from name attributes when the same element contributes both:
the value of the name content attribute for all
exposed embed, form, iframe,
img, and exposed object elements that have a non-empty
name content attribute and are in a document tree with
document as their root;
the value of the id content attribute for all
exposed object elements that have a non-empty
id content attribute and are in a document tree with
document as their root; and
the value of the id content attribute for all
img elements that have both a non-empty id content
attribute and a non-empty name content attribute, and are in a
document tree with document as their root.
To determine the value of a named property
name for a Document, the user agent must return the value obtained using
the following steps:
Let elements be the list of named
elements with the name name that are in a document tree with the
Document as their root.
There will be at least one such element, by definition.
If elements has only one element, and that element is an iframe
element, and that iframe element's nested browsing context is not
null, then return the WindowProxy object of the element's nested browsing
context.
Otherwise, if elements has only one element, return that element.
Otherwise return an HTMLCollection rooted at the Document node,
whose filter matches only named elements with
the name name.
Named elements with the name name, for the purposes of the above algorithm, are those that are either:
embed, form, iframe,
img, or exposed object elements that have a name content attribute whose value is name, orobject elements that have an id content attribute whose value is name, orimg elements that have an id content attribute
whose value is name, and that have a non-empty name
content attribute present also.An embed or object element is said to be exposed if it has
no exposed object ancestor, and, for object elements, is
additionally either not showing its fallback content or has no object or
embed descendants.
The dir attribute on the
Document interface is defined along with the dir
content attribute.
Elements, attributes, and attribute values in HTML are defined (by this specification) to have
certain meanings (semantics). For example, the ol element represents an ordered list,
and the lang attribute represents the language of the content.
These definitions allow HTML processors, such as Web browsers or search engines, to present and use documents and applications in a wide variety of contexts that the author might not have considered.
As a simple example, consider a Web page written by an author who only considered desktop computer Web browsers:
<!DOCTYPE HTML>
< html lang = "en" >
< head >
< title > My Page</ title >
</ head >
< body >
< h1 > Welcome to my page</ h1 >
< p > I like cars and lorries and have a big Jeep!</ p >
< h2 > Where I live</ h2 >
< p > I live in a small hut on a mountain!</ p >
</ body >
</ html > Because HTML conveys meaning, rather than presentation, the same page can also be used by a small browser on a mobile phone, without any change to the page. Instead of headings being in large letters as on the desktop, for example, the browser on the mobile phone might use the same size text for the whole page, but with the headings in bold.
But it goes further than just differences in screen size: the same page could equally be used by a blind user using a browser based around speech synthesis, which instead of displaying the page on a screen, reads the page to the user, e.g. using headphones. Instead of large text for the headings, the speech browser might use a different volume or a slower voice.
That's not all, either. Since the browsers know which parts of the page are the headings, they can create a document outline that the user can use to quickly navigate around the document, using keys for "jump to next heading" or "jump to previous heading". Such features are especially common with speech browsers, where users would otherwise find quickly navigating a page quite difficult.
Even beyond browsers, software can make use of this information. Search engines can use the headings to more effectively index a page, or to provide quick links to subsections of the page from their results. Tools can use the headings to create a table of contents (that is in fact how this very specification's table of contents is generated).
This example has focused on headings, but the same principle applies to all of the semantics in HTML.
Authors must not use elements, attributes, or attribute values for purposes other than their appropriate intended semantic purpose, as doing so prevents software from correctly processing the page.
For example, the following snippet, intended to represent the heading of a corporate site, is non-conforming because the second line is not intended to be a heading of a subsection, but merely a subheading or subtitle (a subordinate heading for the same section).
< body >
< h1 > ACME Corporation</ h1 >
< h2 > The leaders in arbitrary fast delivery since 1920</ h2 >
...The hgroup element is intended for these kinds of situations:
< body >
< hgroup >
< h1 > ACME Corporation</ h1 >
< h2 > The leaders in arbitrary fast delivery since 1920</ h2 >
</ hgroup >
...The document in this next example is similarly non-conforming, despite
being syntactically correct, because the data placed in the cells is clearly
not tabular data, and the cite element mis-used:
<!DOCTYPE HTML>
< html lang = "en-GB" >
< head > < title > Demonstration </ title > </ head >
< body >
< table >
< tr > < td > My favourite animal is the cat. </ td > </ tr >
< tr >
< td >
—< a href = "https://example.org/~ernest/" >< cite > Ernest</ cite ></ a > ,
in an essay from 1992
</ td >
</ tr >
</ table >
</ body >
</ html > This would make software that relies on these semantics fail: for example, a speech browser that allowed a blind user to navigate tables in the document would report the quote above as a table, confusing the user; similarly, a tool that extracted titles of works from pages would extract "Ernest" as the title of a work, even though it's actually a person's name, not a title.
A corrected version of this document might be:
<!DOCTYPE HTML>
< html lang = "en-GB" >
< head > < title > Demonstration </ title > </ head >
< body >
< blockquote >
< p > My favourite animal is the cat. </ p >
</ blockquote >
< p >
—< a href = "https://example.org/~ernest/" > Ernest</ a > ,
in an essay from 1992
</ p >
</ body >
</ html > Authors must not use elements, attributes, or attribute values that are not permitted by this specification or other applicable specifications, as doing so makes it significantly harder for the language to be extended in the future.
In the next example, there is a non-conforming attribute value ("carpet") and a non-conforming attribute ("texture"), which is not permitted by this specification:
< label > Carpet: < input type = "carpet" name = "c" texture = "deep pile" ></ label > Here would be an alternative and correct way to mark this up:
< label > Carpet: < input type = "text" class = "carpet" name = "c" data-texture = "deep pile" ></ label > DOM nodes whose node document's browsing context is null are exempt from all document conformance requirements other than the HTML syntax requirements and XML syntax requirements.
In particular, the template element's template contents's node
document's browsing context is null. For
example, the content model requirements and
attribute value microsyntax requirements do not apply to a template element's
template contents. In this example an img element has attribute values
that are placeholders that would be invalid outside a template element.
< template >
< article >
< img src = "{{src}}" alt = "{{alt}}" >
< h1 ></ h1 >
</ article >
</ template > However, if the above markup were to omit the </h1> end tag, that
would be a violation of the HTML syntax, and would thus be flagged as an
error by conformance checkers.
Through scripting and using other mechanisms, the values of attributes, text, and indeed the entire structure of the document may change dynamically while a user agent is processing it. The semantics of a document at an instant in time are those represented by the state of the document at that instant in time, and the semantics of a document can therefore change over time. User agents must update their presentation of the document as this occurs.
HTML has a progress element that describes a progress bar. If its
"value" attribute is dynamically updated by a script, the UA would update the rendering to show
the progress changing.
The nodes representing HTML elements in the DOM must implement, and expose to scripts, the interfaces listed for them in the relevant sections of this specification. This includes HTML elements in XML documents, even when those documents are in another context (e.g. inside an XSLT transform).
Elements in the DOM represent things; that is, they have intrinsic meaning, also known as semantics.
For example, an ol element represents an ordered list.
Elements can be referenced (referred to) in some way, either
explicitly or implicitly. One way that an element in the DOM can be explicitly referenced is by
giving an id attribute to the element, and then creating a
hyperlink with that id attribute's value as the fragment for the hyperlink's href attribute value. Hyperlinks are not necessary for a
reference, however; any manner of referring to the element in question will suffice.
Consider the following figure element, which is given an id attribute:
< figure id = "module-script-graph" >
< img src = "module-script-graph.svg"
alt = "Module A depends on module B, which depends
on modules C and D." >
< figcaption > Figure 27: a simple module graph</ figcaption >
</ figure > A hyperlink-based reference could be created
using the a element, like so:
As we can see in < a href = "#module-script-graph" > figure 27</ a > , ...However, there are many other ways of referencing the
figure element, such as:
"As depicted in the figure of modules A, B, C, and D..."
"In Figure 27..." (without a hyperlink)
"From the contents of the 'simple module graph' figure..."
"In the figure below..." (but this is discouraged)
The basic interface, from which all the HTML elements' interfaces inherit, and which must be used by elements that have no additional requirements, is
the HTMLElement interface.
[Exposed =Window ,
HTMLConstructor ]
interface HTMLElement : Element {
// metadata attributes
[CEReactions ] attribute DOMString title ;
[CEReactions ] attribute DOMString lang ;
[CEReactions ] attribute boolean translate ;
[CEReactions ] attribute DOMString dir ;
// user interaction
[CEReactions ] attribute boolean hidden ;
void click ();
[CEReactions ] attribute DOMString accessKey ;
readonly attribute DOMString accessKeyLabel ;
[CEReactions ] attribute boolean draggable ;
[CEReactions ] attribute boolean spellcheck ;
[CEReactions ] attribute DOMString autocapitalize ;
[CEReactions ] attribute [TreatNullAs =EmptyString ] DOMString innerText ;
ElementInternals attachInternals ();
};
HTMLElement includes GlobalEventHandlers ;
HTMLElement includes DocumentAndElementEventHandlers ;
HTMLElement includes ElementContentEditable ;
HTMLElement includes HTMLOrSVGElement ;
// Note: intentionally not [HTMLConstructor]
[Exposed =Window ]
interface HTMLUnknownElement : HTMLElement { };The HTMLElement interface holds methods and attributes related to a number of
disparate features, and the members of this interface are therefore described in various different
sections of this specification.
The element interface for an element with name name in the HTML namespace is determined as follows:
If name is applet, bgsound, blink,
isindex, keygen, multicol, nextid, or
spacer, then return HTMLUnknownElement.
If name is acronym, basefont, big,
center, nobr, noembed, noframes,
plaintext, rb, rtc, strike, or
tt, then return HTMLElement.
If name is listing or xmp, then return
HTMLPreElement.
Otherwise, if this specification defines an interface appropriate for the element type corresponding to the local name name, then return that interface.
If other applicable specifications define an appropriate interface for name, then return the interface they define.
If name is a valid custom element name, then return
HTMLElement.
Return HTMLUnknownElement.
The use of HTMLElement instead of HTMLUnknownElement in
the case of valid custom element names is done to
ensure that any potential future upgrades only cause
a linear transition of the element's prototype chain, from HTMLElement to a subclass,
instead of a lateral one, from HTMLUnknownElement to an unrelated subclass.
Features shared between HTML and SVG elements use the HTMLOrSVGElement interface
mixin: [SVG]
interface mixin HTMLOrSVGElement {
[SameObject ] readonly attribute DOMStringMap dataset ;
attribute DOMString nonce ; // intentionally no [CEReactions]
[CEReactions ] attribute boolean autofocus ;
[CEReactions ] attribute long tabIndex ;
void focus (optional FocusOptions options = {});
void blur ();
};To support the custom elements feature, all HTML elements have
special constructor behavior. This is indicated via the [HTMLConstructor] IDL extended attribute.
It indicates that the interface object for the given interface will have a specific behavior when
called, as defined in detail below.
The [HTMLConstructor] extended attribute must take no
arguments, and must not appear on anything other than an interface. It must appear only once on an
interface, and the interface must not be annotated with the [Constructor]
or [NoInterfaceObject] extended attributes. (However, the interface may be
annotated with [NamedConstructor]; there is no conflict there.) It must not
be used on a callback interface.
Interface objects for interfaces annotated with the
[HTMLConstructor] extended attribute must run the following
steps as the function body behavior for both [[Call]] and [[Construct]] invocations of the
corresponding JavaScript function object. When invoked with [[Call]], the NewTarget value is
undefined, and so the algorithm below will immediately throw. When invoked with [[Construct]], the
[[Construct]] newTarget parameter provides the NewTarget value.
Let registry be the current global object's
CustomElementRegistry object.
If NewTarget is equal to the active function object, then throw a
TypeError.
This can occur when a custom element is defined using an element interface as its constructor:
customElements. define( "bad-1" , HTMLButtonElement);
new HTMLButtonElement(); // (1)
document. createElement( "bad-1" ); // (2) In this case, during the execution of HTMLButtonElement (either explicitly, as
in (1), or implicitly, as in (2)), both the active function object and NewTarget
are HTMLButtonElement. If this check was not present, it would be possible to
create an instance of HTMLButtonElement whose local name was bad-1.
Let definition be the entry in registry with constructor equal to NewTarget. If
there is no such definition, then throw a TypeError.
Since there can be no entry in registry with a constructor of undefined, this step also prevents HTML element constructors from being called as functions (since in that case NewTarget will be undefined).
Let is value be null.
If definition's local name is equal to definition's name (i.e., definition is for an autonomous custom element), then:
If the active function object is not HTMLElement, then throw a
TypeError.
This can occur when a custom element is defined to not extend any local names, but
inherits from a non-HTMLElement class:
customElements. define( "bad-2" , class Bad2 extends HTMLParagraphElement {}); In this case, during the (implicit) super() call that occurs when
constructing an instance of Bad2, the active function
object is HTMLParagraphElement, not HTMLElement.
Otherwise (i.e., if definition is for a customized built-in element):
Let valid local names be the list of local names for elements defined in this specification or in other applicable specifications that use the active function object as their element interface.
If valid local names does not contain definition's local name, then throw a
TypeError.
This can occur when a custom element is defined to extend a given local name but inherits from the wrong class:
customElements. define( "bad-3" , class Bad3 extends HTMLQuoteElement {}, { extends : "p" }); In this case, during the (implicit) super() call that occurs when
constructing an instance of Bad3, valid local names is the
list containing q and blockquote, but definition's local name is p,
which is not in that list.
Set is value to definition's name.
Let prototype be Get(NewTarget, "prototype"). Rethrow any exceptions.
If Type(prototype) is not Object, then:
Let realm be GetFunctionRealm(NewTarget).
Set prototype to the interface prototype object of realm whose interface is the same as the interface of the active function object.
The realm of the active function object might not be realm, so we are using the more general concept of "the same interface" across realms; we are not looking for equality of interface objects. This fallback behavior, including using the realm of NewTarget and looking up the appropriate prototype there, is designed to match analogous behavior for the JavaScript built-ins.
If definition's construction stack is empty, then:
Let element be a new element that implements the interface to which the
active function object corresponds, with no attributes, namespace set to the
HTML namespace, local name set to definition's local name, and node
document set to the current global object's associated Document.
Perform element.[[SetPrototypeOf]](prototype). Rethrow any exceptions.
Set element's custom element state to "custom".
Set element's custom element definition to definition.
Set element's is value to is value.
Return element.
This occurs when author script constructs a new custom element directly, e.g.
via new MyCustomElement().
Let element be the last entry in definition's construction stack.
If element is an already
constructed marker, then throw an "InvalidStateError"
DOMException.
This can occur when the author code inside the custom element
constructor non-conformantly creates another
instance of the class being constructed, before calling super():
let doSillyThing = false ;
class DontDoThis extends HTMLElement {
constructor() {
if ( doSillyThing) {
doSillyThing = false ;
new DontDoThis();
// Now the construction stack will contain an already constructed marker.
}
// This will then fail with an "InvalidStateError" DOMException:
super ();
}
} This can also occur when author code inside the custom element constructor non-conformantly calls super()
twice, since per the JavaScript specification, this actually executes the superclass
constructor (i.e. this algorithm) twice, before throwing an error:
class DontDoThisEither extends HTMLElement {
constructor() {
super ();
// This will throw, but not until it has already called into the HTMLElement constructor
super ();
}
} Perform element.[[SetPrototypeOf]](prototype). Rethrow any exceptions.
Replace the last entry in definition's construction stack with an already constructed marker.
Return element.
This step is normally reached when upgrading a custom element; the existing element is
returned, so that the super() call inside the custom element
constructor assigns that existing element to this.
In addition to the constructor behavior implied by [HTMLConstructor], some elements also have named constructors (which are really factory functions with a modified prototype property).
Named constructors for HTML elements can also be used in an extends
clause when defining a custom element constructor:
class AutoEmbiggenedImage extends Image {
constructor( width, height) {
super ( width * 10 , height * 10 );
}
}
customElements. define( "auto-embiggened" , AutoEmbiggenedImage, { extends : "img" });
const image = new AutoEmbiggenedImage( 15 , 20 );
console. assert( image. width === 150 );
console. assert( image. height === 200 ); Each element in this specification has a definition that includes the following information:
A list of categories to which the element belongs. These are used when defining the content models for each element.
A non-normative description of where the element can be used. This information is redundant with the content models of elements that allow this one as a child, and is provided only as a convenience.
For simplicity, only the most specific expectations are listed. For example, an element that is both flow content and phrasing content can be used anywhere that either flow content or phrasing content is expected, but since anywhere that flow content is expected, phrasing content is also expected (since all phrasing content is flow content), only "where phrasing content is expected" will be listed.
A normative description of what content must be included as children and descendants of the element.
A non-normative description of whether, in the text/html syntax, the
start and end tags can
be omitted. This information is redundant with the normative requirements given in the optional tags section, and is provided in the element
definitions only as a convenience.
A normative list of attributes that may be specified on the element (except where otherwise disallowed), along with non-normative descriptions of those attributes. (The content to the left of the dash is normative, the content to the right of the dash is not.)
A normative definition of a DOM interface that such elements must implement.
This is then followed by a description of what the element represents, along with any additional normative conformance criteria that may apply to authors and implementations. Examples are sometimes also included.
An attribute value is a string. Except where otherwise specified, attribute values on HTML elements may be any string value, including the empty string, and there is no restriction on what text can be specified in such attribute values.
Each element defined in this specification has a content model: a description of the element's expected contents. An HTML element must have contents that match the requirements described in the element's content model. The contents of an element are its children in the DOM.
ASCII whitespace is always allowed between elements. User agents represent these
characters between elements in the source markup as Text nodes in the DOM. Empty Text nodes and
Text nodes consisting of just sequences of those characters are considered
inter-element whitespace.
Inter-element whitespace, comment nodes, and processing instruction nodes must be ignored when establishing whether an element's contents match the element's content model or not, and must be ignored when following algorithms that define document and element semantics.
Thus, an element A is said to be preceded or followed
by a second element B if A and B have
the same parent node and there are no other element nodes or Text nodes (other than
inter-element whitespace) between them. Similarly, a node is the only child of
an element if that element contains no other nodes other than inter-element
whitespace, comment nodes, and processing instruction nodes.
Authors must not use HTML elements anywhere except where they are explicitly allowed, as defined for each element, or as explicitly required by other specifications. For XML compound documents, these contexts could be inside elements from other namespaces, if those elements are defined as providing the relevant contexts.
The Atom Syndication Format defines a content element. When its type attribute has the value
xhtml, The Atom Syndication Format requires that it contain a
single HTML div element. Thus, a div element is allowed in that context,
even though this is not explicitly normatively stated by this specification. [ATOM]
In addition, HTML elements may be orphan nodes (i.e. without a parent node).
For example, creating a td element and storing it in a global variable in a
script is conforming, even though td elements are otherwise only supposed to be used
inside tr elements.
var data = {
name: "Banana" ,
cell: document. createElement( 'td' ),
}; When an element's content model is nothing, the
element must contain no Text nodes (other than inter-element whitespace)
and no element nodes.
Most HTML elements whose content model is "nothing" are also, for convenience, void elements (elements that have no end tag in the HTML syntax). However, these are entirely separate concepts.
Each element in HTML falls into zero or more categories that group elements with similar characteristics together. The following broad categories are used in this specification:
Some elements also fall into other categories, which are defined in other parts of this specification.
These categories are related as follows:
Sectioning content, heading content, phrasing content, embedded content, and interactive content are all types of flow content. Metadata is sometimes flow content. Metadata and interactive content are sometimes phrasing content. Embedded content is also a type of phrasing content, and sometimes is interactive content.
Other categories are also used for specific purposes, e.g. form controls are specified using a number of categories to define common requirements. Some elements have unique requirements and do not fit into any particular category.
Metadata content is content that sets up the presentation or behavior of the rest of the content, or that sets up the relationship of the document with other documents, or that conveys other "out of band" information.
Elements from other namespaces whose semantics are primarily metadata-related (e.g. RDF) are also metadata content.
Thus, in the XML serialization, one can use RDF, like this:
< html xmlns = "http://www.w3.org/1999/xhtml"
xmlns:r = "http://www.w3.org/1999/02/22-rdf-syntax-ns#" xml:lang = "en" >
< head >
< title > Hedral's Home Page</ title >
< r:RDF >
< Person xmlns = "http://www.w3.org/2000/10/swap/pim/contact#"
r:about = "https://hedral.example.com/#" >
< fullName > Cat Hedral</ fullName >
< mailbox r:resource = "mailto:hedral@damowmow.com" />
< personalTitle > Sir</ personalTitle >
</ Person >
</ r:RDF >
</ head >
< body >
< h1 > My home page</ h1 >
< p > I like playing with string, I guess. Sister says squirrels are fun
too so sometimes I follow her to play with them.</ p >
</ body >
</ html > This isn't possible in the HTML serialization, however.
Most elements that are used in the body of documents and applications are categorized as flow content.
aabbraddressarea (if it is a descendant of a map element)articleasideaudiobbdibdoblockquotebrbuttoncanvascitecodedatadatalistdeldetailsdfndialogdivdlemembedfieldsetfigurefooterformh1h2h3h4h5h6headerhgrouphriiframeimginputinskbdlabellink (if it is allowed in the body)main (if it is a hierarchically correct main element)mapmarkmathmenumeta (if the itemprop attribute is present)meternavnoscriptobjectoloutputppicturepreprogressqrubyssampscriptsectionselectslotsmallspanstrongsubsupsvgtabletemplatetextareatimeuulvarvideowbrSectioning content is content that defines the scope of headings and footers.
Each sectioning content element potentially has a heading and an outline. See the section on headings and sections for further details.
There are also certain elements that are sectioning roots. These are distinct from sectioning content, but they can also have an outline.
Heading content defines the header of a section (whether explicitly marked up using sectioning content elements, or implied by the heading content itself).
Phrasing content is the text of the document, as well as elements that mark up that text at the intra-paragraph level. Runs of phrasing content form paragraphs.
aabbrarea (if it is a descendant of a map element)audiobbdibdobrbuttoncanvascitecodedatadatalistdeldfnemembediiframeimginputinskbdlabellink (if it is allowed in the body)mapmarkmathmeta (if the itemprop attribute is present)meternoscriptobjectoutputpictureprogressqrubyssampscriptselectslotsmallspanstrongsubsupsvgtemplatetextareatimeuvarvideowbrMost elements that are categorized as phrasing content can only contain elements that are themselves categorized as phrasing content, not any flow content.
Text, in the context of content models, means either nothing,
or Text nodes. Text is sometimes used as a content
model on its own, but is also phrasing content, and can be inter-element
whitespace (if the Text nodes are empty or contain just ASCII
whitespace).
Text nodes and attribute values must consist of scalar
values, excluding noncharacters, and controls other than ASCII whitespace.
This specification includes extra constraints on the exact value of Text nodes and
attribute values depending on their precise context.
Embedded content is content that imports another resource into the document, or content from another vocabulary that is inserted into the document.
Elements that are from namespaces other than the HTML namespace and that convey content but not metadata, are embedded content for the purposes of the content models defined in this specification. (For example, MathML, or SVG.)
Some embedded content elements can have fallback content: content that is to be used when the external resource cannot be used (e.g. because it is of an unsupported format). The element definitions state what the fallback is, if any.
Interactive content is content that is specifically intended for user interaction.
a (if the href attribute is present)audio (if the controls attribute is present)buttondetailsembediframeimg (if the usemap attribute is present)input (if the type attribute is not in the state)labelobject (if the usemap attribute is present)selecttextareavideo (if the controls attribute is present)The tabindex attribute can also make any element into
interactive content.
As a general rule, elements whose content model allows any flow content or phrasing content should have at least one node in its contents that is palpable content and that does not have the attribute specified.
Palpable content makes an element non-empty by providing either
some descendant non-empty text, or else something users can
hear (audio elements) or view (video or img or
canvas elements) or otherwise interact with (for example, interactive form
controls).
This requirement is not a hard requirement, however, as there are many cases where an element can be empty legitimately, for example when it is used as a placeholder which will later be filled in by a script, or when the element is part of a template and would on most pages be filled in but on some pages is not relevant.
Conformance checkers are encouraged to provide a mechanism for authors to find elements that fail to fulfill this requirement, as an authoring aid.
The following elements are palpable content:
aabbraddressarticleasideaudio (if the controls attribute is present)bbdibdoblockquotebuttoncanvascitecodedatadetailsdfndivdl (if the element's children include at least one name-value group)emembedfieldsetfigurefooterformh1h2h3h4h5h6headerhgroupiiframeimginput (if the type attribute is not in the state)inskbdlabelmainmapmarkmathmenu (if the element's children include at least one li element)meternavobjectol (if the element's children include at least one li element)outputppreprogressqrubyssampsectionselectsmallspanstrongsubsupsvgtabletextareatimeuul (if the element's children include at least one li element)varvideoScript-supporting elements are those that do not represent anything themselves (i.e. they are not rendered), but are used to support scripts, e.g. to provide functionality for the user.
The following elements are script-supporting elements:
Some elements are described as transparent; they have "transparent" in the description of their content model. The content model of a transparent element is derived from the content model of its parent element: the elements required in the part of the content model that is "transparent" are the same elements as required in the part of the content model of the parent of the transparent element in which the transparent element finds itself.
For instance, an ins element inside a ruby element cannot contain an
rt element, because the part of the ruby element's content model that
allows ins elements is the part that allows phrasing content, and the
rt element is not phrasing content.
In some cases, where transparent elements are nested in each other, the process has to be applied iteratively.
Consider the following markup fragment:
< p >< object >< param >< ins >< map >< a href = "/" > Apples</ a ></ map ></ ins ></ object ></ p > To check whether "Apples" is allowed inside the a element, the content models are
examined. The a element's content model is transparent, as is the map
element's, as is the ins element's, as is the part of the object
element's in which the ins element is found. The object element is
found in the p element, whose content model is phrasing content. Thus,
"Apples" is allowed, as text is phrasing content.
When a transparent element has no parent, then the part of its content model that is "transparent" must instead be treated as accepting any flow content.
The term paragraph as defined in this section is used for more than
just the definition of the p element. The paragraph concept defined here
is used to describe how to interpret documents. The p element is merely one of
several ways of marking up a paragraph.
A paragraph is typically a run of phrasing content that forms a block of text with one or more sentences that discuss a particular topic, as in typography, but can also be used for more general thematic grouping. For instance, an address is also a paragraph, as is a part of a form, a byline, or a stanza in a poem.
In the following example, there are two paragraphs in a section. There is also a heading, which contains phrasing content that is not a paragraph. Note how the comments and inter-element whitespace do not form paragraphs.
< section >
< h1 > Example of paragraphs</ h1 >
This is the < em > first</ em > paragraph in this example.
< p > This is the second.</ p >
<!-- This is not a paragraph. -->
</ section > Paragraphs in flow content are defined relative to what the document looks like
without the a, ins, del, and map elements
complicating matters, since those elements, with their hybrid content models, can straddle
paragraph boundaries, as shown in the first two examples below.
Generally, having elements straddle paragraph boundaries is best avoided. Maintaining such markup can be difficult.
The following example takes the markup from the earlier example and puts ins and
del elements around some of the markup to show that the text was changed (though in
this case, the changes admittedly don't make much sense). Notice how this example has exactly the
same paragraphs as the previous one, despite the ins and del elements
— the ins element straddles the heading and the first paragraph, and the
del element straddles the boundary between the two paragraphs.
< section >
< ins >< h1 > Example of paragraphs</ h1 >
This is the < em > first</ em > paragraph in</ ins > this example< del > .
< p > This is the second.</ p ></ del >
<!-- This is not a paragraph. -->
</ section > Let view be a view of the DOM that replaces all a,
ins, del, and map elements in the document with their contents. Then, in view, for each run
of sibling phrasing content nodes uninterrupted by other types of content, in an
element that accepts content other than phrasing content as well as phrasing
content, let first be the first node of the run, and let last be the last node of the run. For each such run that consists of at least one
node that is neither embedded content nor inter-element whitespace, a
paragraph exists in the original DOM from immediately before first to
immediately after last. (Paragraphs can thus span across a,
ins, del, and map elements.)
Conformance checkers may warn authors of cases where they have paragraphs that overlap each
other (this can happen with object, video, audio, and
canvas elements, and indirectly through elements in other namespaces that allow HTML
to be further embedded therein, like SVG svg or MathML
math).
A paragraph is also formed explicitly by p elements.
The p element can be used to wrap individual paragraphs when there
would otherwise not be any content other than phrasing content to separate the paragraphs from
each other.
In the following example, the link spans half of the first paragraph, all of the heading separating the two paragraphs, and half of the second paragraph. It straddles the paragraphs and the heading.
< header >
Welcome!
< a href = "about.html" >
This is home of...
< h1 > The Falcons!</ h1 >
The Lockheed Martin multirole jet fighter aircraft!
</ a >
This page discusses the F-16 Fighting Falcon's innermost secrets.
</ header > Here is another way of marking this up, this time showing the paragraphs explicitly, and splitting the one link element into three:
< header >
< p > Welcome! < a href = "about.html" > This is home of...</ a ></ p >
< h1 >< a href = "about.html" > The Falcons!</ a ></ h1 >
< p >< a href = "about.html" > The Lockheed Martin multirole jet
fighter aircraft!</ a > This page discusses the F-16 Fighting
Falcon's innermost secrets.</ p >
</ header > It is possible for paragraphs to overlap when using certain elements that define fallback content. For example, in the following section:
< section >
< h1 > My Cats</ h1 >
You can play with my cat simulator.
< object data = "cats.sim" >
To see the cat simulator, use one of the following links:
< ul >
< li >< a href = "cats.sim" > Download simulator file</ a >
< li >< a href = "https://sims.example.com/watch?v=LYds5xY4INU" > Use online simulator</ a >
</ ul >
Alternatively, upgrade to the Mellblom Browser.
</ object >
I'm quite proud of it.
</ section > There are five paragraphs:
object element.The first paragraph is overlapped by the other four. A user agent that supports the "cats.sim" resource will only show the first one, but a user agent that shows the fallback will confusingly show the first sentence of the first paragraph as if it was in the same paragraph as the second one, and will show the last paragraph as if it was at the start of the second sentence of the first paragraph.
To avoid this confusion, explicit p elements can be used. For example:
< section >
< h1 > My Cats</ h1 >
< p > You can play with my cat simulator.</ p >
< object data = "cats.sim" >
< p > To see the cat simulator, use one of the following links:</ p >
< ul >
< li >< a href = "cats.sim" > Download simulator file</ a >
< li >< a href = "https://sims.example.com/watch?v=LYds5xY4INU" > Use online simulator</ a >
</ ul >
< p > Alternatively, upgrade to the Mellblom Browser.</ p >
</ object >
< p > I'm quite proud of it.</ p >
</ section > The following attributes are common to and may be specified on all HTML elements (even those not defined in this specification):
accesskeyautocapitalizeautofocuscontenteditabledirdraggableenterkeyhintinputmodeisitemiditempropitemrefitemscopeitemtypelangnoncespellcheckstyletabindextitletranslateThese attributes are only defined by this specification as attributes for HTML elements. When this specification refers to elements having these attributes, elements from namespaces that are not defined as having these attributes must not be considered as being elements with these attributes.
For example, in the following XML fragment, the "bogus" element does not
have a dir attribute as defined in this specification, despite
having an attribute with the literal name "dir". Thus, the
directionality of the inner-most span element is 'rtl', inherited from the div element indirectly through
the "bogus" element.
< div xmlns = "http://www.w3.org/1999/xhtml" dir = "rtl" >
< bogus xmlns = "https://example.net/ns" dir = "ltr" >
< span xmlns = "http://www.w3.org/1999/xhtml" >
</ span >
</ bogus >
</ div > DOM standard defines the user agent requirements for the class, id, and slot
attributes for any element in any namespace. [DOM]
The class, id, and slot attributes may be specified on all HTML elements.
When specified on HTML elements, the class
attribute must have a value that is a set of space-separated tokens representing the
various classes that the element belongs to.
Assigning classes to an element affects class matching in selectors in CSS, the getElementsByClassName() method in the DOM,
and other such features.
There are no additional restrictions on the tokens authors can use in the class attribute, but authors are encouraged to use values that describe
the nature of the content, rather than values that describe the desired presentation of the
content.
When specified on HTML elements, the id attribute
value must be unique amongst all the IDs in the element's
tree and must contain at least one character. The value must not contain any
ASCII whitespace.
The id attribute specifies its element's unique identifier (ID).
There are no other restrictions on what form an ID can take; in particular, IDs can consist of just digits, start with a digit, start with an underscore, consist of just punctuation, etc.
An element's unique identifier can be used for a variety of purposes, most notably as a way to link to specific parts of a document using fragments, as a way to target an element when scripting, and as a way to style a specific element from CSS.
Identifiers are opaque strings. Particular meanings should not be derived from the value of the
id attribute.
There are no conformance requirements for the slot attribute
specific to HTML elements.
The slot attribute is used to assign a
slot to an element: an element with a slot attribute is
assigned to the slot
created by the slot element whose name
attribute's value matches that slot attribute's value — but only
if that slot element finds itself in the shadow tree whose
root's host has the corresponding
slot attribute value.
To enable assistive technology products to expose a more fine-grained interface than is
otherwise possible with HTML elements and attributes, a set of annotations
for assistive technology products can be specified (the ARIA role and aria-* attributes). [ARIA]
The following event handler content attributes may be specified on any HTML element:
onabortonauxclickonblur*oncanceloncanplayoncanplaythroughonchangeonclickoncloseoncontextmenuoncopyoncuechangeoncutondblclickondragondragendondragenterondragexitondragleaveondragoverondragstartondropondurationchangeonemptiedonendedonerror*onfocus*onformdataoninputoninvalidonkeydownonkeypressonkeyuponload*onloadeddataonloadedmetadataonloadstartonmousedownonmouseenteronmouseleaveonmousemoveonmouseoutonmouseoveronmouseuponpasteonpauseonplayonplayingonprogressonratechangeonresetonresize*onscroll*onsecuritypolicyviolationonseekedonseekingonselectonstalledonsubmitonsuspendontimeupdateontoggleonvolumechangeonwaitingonwheelThe attributes marked with an asterisk have a different meaning when specified on
body elements as those elements expose event handlers of the
Window object with the same names.
While these attributes apply to all elements, they are not useful on all elements.
For example, only media elements will ever receive a volumechange event fired by the user agent.
Custom data attributes (e.g. data-foldername or data-msgid) can be specified on any
HTML element, to store custom data, state, annotations, and
similar, specific to the page.
In HTML documents, elements in the HTML namespace may have an xmlns attribute specified, if, and only if, it has the exact value "http://www.w3.org/1999/xhtml". This does not apply to XML
documents.
In HTML, the xmlns attribute has absolutely no effect. It
is basically a talisman. It is allowed merely to make migration to and from XML mildly easier.
When parsed by an HTML parser, the attribute ends up in no namespace, not the "http://www.w3.org/2000/xmlns/" namespace like namespace declaration attributes in
XML do.
In XML, an xmlns attribute is part of the namespace
declaration mechanism, and an element cannot actually have an xmlns
attribute in no namespace specified.
XML also allows the use of the xml:space
attribute in the XML namespace on any element in an XML
document. This attribute has no effect on HTML elements, as the default
behavior in HTML is to preserve whitespace. [XML]
There is no way to serialize the xml:space
attribute on HTML elements in the text/html syntax.
title attributeThe title attribute represents
advisory information for the element, such as would be appropriate for a tooltip. On a link, this
could be the title or a description of the target resource; on an image, it could be the image
credit or a description of the image; on a paragraph, it could be a footnote or commentary on the
text; on a citation, it could be further information about the source; on interactive
content, it could be a label for, or instructions for, use of the element; and so forth.
The value is text.
Relying on the title attribute is currently
discouraged as many user agents do not expose the attribute in an accessible manner as required by
this specification (e.g., requiring a pointing device such as a mouse to cause a tooltip to
appear, which excludes keyboard-only users and touch-only users, such as anyone with a modern
phone or tablet).
If this attribute is omitted from an element, then it implies that the title attribute of the nearest ancestor HTML element with a title attribute set is also
relevant to this element. Setting the attribute overrides this, explicitly stating that the
advisory information of any ancestors is not relevant to this element. Setting the attribute to
the empty string indicates that the element has no advisory information.
If the title attribute's value contains U+000A LINE FEED (LF)
characters, the content is split into multiple lines. Each U+000A LINE FEED (LF) character
represents a line break.
Caution is advised with respect to the use of newlines in title attributes.
For instance, the following snippet actually defines an abbreviation's expansion with a line break in it:
< p > My logs show that there was some interest in < abbr title = "Hypertext
Transport Protocol" > HTTP</ abbr > today.</ p > Some elements, such as link, abbr, and input, define
additional semantics for the title attribute beyond the semantics
described above.
The advisory information of an element is the value that the following algorithm returns, with the algorithm being aborted once a value is returned. When the algorithm returns the empty string, then there is no advisory information.
If the element has a title attribute, then return its
value.
If the element has a parent element, then return the parent element's advisory information.
Return the empty string.
User agents should inform the user when elements have advisory information, otherwise the information would not be discoverable.
The title IDL attribute must reflect the
title content attribute.
lang and xml:lang attributesThe lang attribute (in no namespace) specifies the
primary language for the element's contents and for any of the element's attributes that contain
text. Its value must be a valid BCP 47 language tag, or the empty string. Setting the attribute to
the empty string indicates that the primary language is unknown. [BCP47]
The lang attribute in the XML
namespace is defined in XML. [XML]
If these attributes are omitted from an element, then the language of this element is the same as the language of its parent element, if any.
The lang attribute in no namespace may be used on any HTML element.
The lang attribute in the XML
namespace may be used on HTML elements in XML documents,
as well as elements in other namespaces if the relevant specifications allow it (in particular,
MathML and SVG allow lang attributes in the
XML namespace to be specified on their elements). If both the lang attribute in no namespace and the lang attribute in the XML namespace are specified on the same
element, they must have exactly the same value when compared in an ASCII
case-insensitive manner.
Authors must not use the lang attribute in
the XML namespace on HTML elements in HTML
documents. To ease migration to and from XML, authors may specify an attribute in no
namespace with no prefix and with the literal localname "xml:lang" on
HTML elements in HTML documents, but such attributes must only be
specified if a lang attribute in no namespace is also specified,
and both attributes must have the same value when compared in an ASCII
case-insensitive manner.
The attribute in no namespace with no prefix and with the literal localname "xml:lang" has no effect on language processing.
To determine the language of a node, user agents must look at the nearest ancestor
element (including the element itself if the node is an element) that has a lang attribute in the XML
namespace set or is an HTML element and has a
lang in no namespace attribute set. That attribute specifies the
language of the node (regardless of its value).
If both the lang attribute in no namespace and the lang attribute in the XML
namespace are set on an element, user agents must use the lang attribute in the XML
namespace, and the lang attribute in no namespace
must be ignored for the purposes of determining the element's
language.
If node's inclusive ancestors do not have either attribute set, but there is a pragma-set default language set, then that is the language of the node. If there is no pragma-set default language set, then language information from a higher-level protocol (such as HTTP), if any, must be used as the final fallback language instead. In the absence of any such language information, and in cases where the higher-level protocol reports multiple languages, the language of the node is unknown, and the corresponding language tag is the empty string.
If the resulting value is not a recognized language tag, then it must be treated as an unknown language having the given language tag, distinct from all other languages. For the purposes of round-tripping or communicating with other services that expect language tags, user agents should pass unknown language tags through unmodified, and tagged as being BCP 47 language tags, so that subsequent services do not interpret the data as another type of language description. [BCP47]
Thus, for instance, an element with lang="xyzzy" would be
matched by the selector :lang(xyzzy) (e.g. in CSS), but it would not be
matched by :lang(abcde), even though both are equally invalid. Similarly, if
a Web browser and screen reader working in unison communicated about the language of the element,
the browser would tell the screen reader that the language was "xyzzy", even if it knew it was
invalid, just in case the screen reader actually supported a language with that tag after all.
Even if the screen reader supported both BCP 47 and another syntax for encoding language names,
and in that other syntax the string "xyzzy" was a way to denote the Belarusian language, it would
be incorrect for the screen reader to then start treating text as Belarusian, because
"xyzzy" is not how Belarusian is described in BCP 47 codes (BCP 47 uses the code "be" for
Belarusian).
If the resulting value is the empty string, then it must be interpreted as meaning that the language of the node is explicitly unknown.
User agents may use the element's language to determine proper processing or rendering (e.g. in the selection of appropriate fonts or pronunciations, for dictionary selection, or for the user interfaces of form controls such as date pickers).
The lang IDL attribute must reflect the
lang content attribute in no namespace.
translate attributeThe translate attribute is an enumerated
attribute that is used to specify whether an element's attribute values and the values of
its Text node children are to be translated when the page is localized, or whether to
leave them unchanged.
The attribute's keywords are the empty string, yes, and no. The empty string and the yes keyword map to the
yes state. The no keyword maps to the no state. In addition,
there is a third state, the inherit state, which is the missing value default and the invalid value default.
Each element (even non-HTML elements) has a translation mode, which is in either the
translate-enabled state or the no-translate state. If an HTML element's translate
attribute is in the yes state, then the element's translation mode is in the
translate-enabled state; otherwise, if the element's translate attribute is in the no state, then the element's
translation mode is in the no-translate state. Otherwise, either the
element's translate attribute is in the inherit state,
or the element is not an HTML element and thus does not have a
translate attribute; in either case, the element's
translation mode is in the same state as its parent element's, if any, or in the
translate-enabled state, if the element is a document element.
When an element is in the translate-enabled state, the element's translatable
attributes and the values of its Text node children are to be translated when
the page is localized.
When an element is in the no-translate state, the element's attribute values and the
values of its Text node children are to be left as-is when the page is localized,
e.g. because the element contains a person's name or a name of a computer program.
The following attributes are translatable attributes:
abbr on th elementsalt on area,
img, and
input elementscontent on meta elements, if the name attribute specifies a metadata name whose value is known to be translatabledownload on a and
area elementslabel on optgroup,
option, and
track elementslang on HTML elements; must be "translated" to match the language used in the translationplaceholder on input and
textarea elementssrcdoc on iframe elements; must be parsed and recursively processedstyle on HTML elements; must be parsed and
recursively processed (e.g. for the values of 'content' properties)title on all HTML elementsvalue on input elements with a
type attribute in the Button state
or the Reset Button stateOther specifications may define other attributes that are also translatable
attributes. For example, ARIA would define the aria-label attribute as translatable.
The translate IDL attribute must, on getting,
return true if the element's translation mode is translate-enabled, and
false otherwise. On setting, it must set the content attribute's value to "yes" if the new value is true, and set the content attribute's value to "no" otherwise.
In this example, everything in the document is to be translated when the page is localized, except the sample keyboard input and sample program output:
<!DOCTYPE HTML>
< html lang = en > <!-- default on the document element is translate=yes -->
< head >
< title > The Bee Game</ title > <!-- implied translate=yes inherited from ancestors -->
</ head >
< body >
< p > The Bee Game is a text adventure game in English.</ p >
< p > When the game launches, the first thing you should do is type
< kbd translate = no > eat honey</ kbd > . The game will respond with:</ p >
< pre >< samp translate = no > Yum yum! That was some good honey!</ samp ></ pre >
</ body >
</ html > dir attributeThe dir attribute specifies the element's text directionality.
The attribute is an enumerated attribute with the following keywords and states:
ltr keyword, which maps to the ltr stateIndicates that the contents of the element are explicitly directionally isolated left-to-right text.
rtl keyword, which maps to the rtl stateIndicates that the contents of the element are explicitly directionally isolated right-to-left text.
auto keyword, which maps to the auto stateIndicates that the contents of the element are explicitly directionally isolated text, but that the direction is to be determined programmatically using the contents of the element (as described below).
The heuristic used by this state is very crude (it just looks at the first character with a strong directionality, in a manner analogous to the Paragraph Level determination in the bidirectional algorithm). Authors are urged to only use this value as a last resort when the direction of the text is truly unknown and no better server-side heuristic can be applied. [BIDI]
For textarea and pre elements, the heuristic is
applied on a per-paragraph level.
The attribute has no invalid value default and no missing value default.
The directionality of an element (any element, not just an HTML element) is either 'ltr' or 'rtl', and is determined as per the first appropriate set of steps from the following list:
dir attribute is in the ltr statedir
attribute is not in a defined state (i.e. it is not present or has an invalid value)input element whose type attribute is in the Telephone state, and the dir
attribute is not in a defined state (i.e. it is not present or has an invalid value)The directionality of the element is 'ltr'.
dir attribute is in the rtl stateThe directionality of the element is 'rtl'.
input element whose type attribute is in the Text, Search,
Telephone, URL, or E-mail
state, and the dir attribute is in the auto statetextarea element and the dir
attribute is in the auto stateIf the element's value contains a character of bidirectional character type AL or R, and there is no character of bidirectional character type L anywhere before it in the element's value, then the directionality of the element is 'rtl'. [BIDI]
Otherwise, if the element's value is not the empty string, or if the element is a document element, the directionality of the element is 'ltr'.
Otherwise, the directionality of the element is the same as the element's parent element's directionality.
dir attribute is in the auto statebdi element and the dir
attribute is not in a defined state (i.e. it is not present or has an invalid value)Find the first character in tree order that matches the following criteria:
The character is from a Text node that is a descendant of the element whose
directionality is being determined.
The character is of bidirectional character type L, AL, or R. [BIDI]
The character is not in a Text node that has an ancestor element that is a
descendant of the element whose directionality is
being determined and that is either:
If such a character is found and it is of bidirectional character type AL or R, the directionality of the element is 'rtl'.
If such a character is found and it is of bidirectional character type L, the directionality of the element is 'ltr'.
Otherwise, if the element is a document element, the directionality of the element is 'ltr'.
Otherwise, the directionality of the element is the same as the element's parent element's directionality.
dir attribute is
not in a defined state (i.e. it is not present or has an invalid value)The directionality of the element is the same as the element's parent element's directionality.
Since the dir attribute is only defined for
HTML elements, it cannot be present on elements from other namespaces. Thus, elements
from other namespaces always just inherit their directionality from their parent element, or, if they don't have one,
default to 'ltr'.
This attribute has rendering requirements involving the bidirectional algorithm.
The directionality of an attribute of an HTML element, which is used when the text of that attribute is to be included in the rendering in some manner, is determined as per the first appropriate set of steps from the following list:
dir attribute is in the auto
stateFind the first character (in logical order) of the attribute's value that is of bidirectional character type L, AL, or R. [BIDI]
If such a character is found and it is of bidirectional character type AL or R, the directionality of the attribute is 'rtl'.
Otherwise, the directionality of the attribute is 'ltr'.
The following attributes are directionality-capable attributes:
abbr on th elementsalt on area,
img, and
input elementscontent on meta elements, if the name attribute specifies a metadata name whose value is primarily intended to be human-readable rather than machine-readablelabel on optgroup,
option, and
track elementsplaceholder on input and
textarea elementstitle on all HTML elementsdir [ = value ]Returns the html element's dir attribute's value, if any.
Can be set, to either "ltr", "rtl", or "auto" to replace the html element's dir attribute's value.
If there is no html element, returns the empty string and ignores new values.
The dir IDL attribute on an element must
reflect the dir content attribute of that element,
limited to only known values.
The dir IDL attribute on Document
objects must reflect the dir content attribute of
the html element, if any, limited to only known values. If
there is no such element, then the attribute must return the empty string and do nothing on
setting.
Authors are strongly encouraged to use the dir
attribute to indicate text direction rather than using CSS, since that way their documents will
continue to render correctly even in the absence of CSS (e.g. as interpreted by search
engines).
This markup fragment is of an IM conversation.
< p dir = auto class = "u1" >< b >< bdi > Student</ bdi > :</ b > How do you write "What's your name?" in Arabic?</ p >
< p dir = auto class = "u2" >< b >< bdi > Teacher</ bdi > :</ b > ما اسمك؟</ p >
< p dir = auto class = "u1" >< b >< bdi > Student</ bdi > :</ b > Thanks.</ p >
< p dir = auto class = "u2" >< b >< bdi > Teacher</ bdi > :</ b > That's written "شكرًا".</ p >
< p dir = auto class = "u2" >< b >< bdi > Teacher</ bdi > :</ b > Do you know how to write "Please"?</ p >
< p dir = auto class = "u1" >< b >< bdi > Student</ bdi > :</ b > "من فضلك", right?</ p > Given a suitable style sheet and the default alignment styles for the p element,
namely to align the text to the start edge of the paragraph, the resulting rendering could
be as follows:
As noted earlier, the auto value is not a panacea. The
final paragraph in this example is misinterpreted as being right-to-left text, since it begins
with an Arabic character, which causes the "right?" to be to the left of the Arabic text.
style attributeAll HTML elements may have the style content
attribute set. This is a style attribute as defined by
CSS Style Attributes. [CSSATTR]
In user agents that support CSS, the attribute's value must be parsed when the attribute is added or has its value changed, according to the rules given for style attributes. [CSSATTR]
However, if the Should element's inline behavior be blocked by Content Security
Policy? algorithm returns "Blocked" when executed upon the
attribute's element, "style attribute", and the attribute's
value, then the style rules defined in the attribute's value must not be applied to the
element. [CSP]
Documents that use style attributes on any of their elements
must still be comprehensible and usable if those attributes were removed.
In particular, using the style attribute to hide
and show content, or to convey meaning that is otherwise not included in the document, is
non-conforming. (To hide and show content, use the
attribute.)
styleReturns a CSSStyleDeclaration object for the element's style attribute.
The style IDL attribute is defined in CSS Object
Model (CSSOM). [CSSOM]
In the following example, the words that refer to colors are marked up using the
span element and the style attribute to make those
words show up in the relevant colors in visual media.
< p > My sweat suit is < span style = "color: green; background:
transparent" > green</ span > and my eyes are < span style = "color: blue;
background: transparent" > blue</ span > .</ p > data-* attributesSupport: datasetChrome for Android 75+Chrome 7+iOS Safari 5.0+Samsung Internet 4+UC Browser for Android 12.12+Firefox 6+Safari 5.1+IE 11+Edge 12+Opera Mini (limited) all+Opera 11.1+Android Browser 3+
Source: caniuse.com
A custom data attribute is an attribute in no namespace whose name starts with the
string "data-", has at least one character after the
hyphen, is XML-compatible, and contains no ASCII
upper alphas.
All attribute names on HTML elements in HTML documents get ASCII-lowercased automatically, so the restriction on ASCII uppercase letters doesn't affect such documents.
Custom data attributes are intended to store custom data, state, annotations, and similar, private to the page or application, for which there are no more appropriate attributes or elements.
These attributes are not intended for use by software that is not known to the administrators of the site that uses the attributes. For generic extensions that are to be used by multiple independent tools, either this specification should be extended to provide the feature explicitly, or a technology like microdata should be used (with a standardized vocabulary).
For instance, a site about music could annotate list items representing tracks in an album with custom data attributes containing the length of each track. This information could then be used by the site itself to allow the user to sort the list by track length, or to filter the list for tracks of certain lengths.
< ol >
< li data-length = "2m11s" > Beyond The Sea</ li >
...
</ ol > It would be inappropriate, however, for the user to use generic software not associated with that music site to search for tracks of a certain length by looking at this data.
This is because these attributes are intended for use by the site's own scripts, and are not a generic extension mechanism for publicly-usable metadata.
Similarly, a page author could write markup that provides information for a translation tool that they are intending to use:
< p > The third < span data-mytrans-de = "Anspruch" > claim</ span > covers the case of < span
translate = "no" > HTML</ span > markup.</ p > In this example, the "data-mytrans-de" attribute gives specific text
for the MyTrans product to use when translating the phrase "claim" to German. However, the
standard translate attribute is used to tell it that in all
languages, "HTML" is to remain unchanged. When a standard attribute is available, there is no
need for a custom data attribute to be used.
In this example, custom data attributes are used to store the result of a feature detection
for PaymentRequest, which could be used in CSS to style a checkout page
differently.
< script >
if ( 'PaymentRequest' in window) {
document. documentElement. dataset. hasPaymentRequest = '' ;
}
</ script > Here, the data-has-payment-request attribute is effectively being used
as a boolean attribute; it is enough to check the presence of the attribute.
However, if the author so wishes, it could later be populated with some value, maybe to indicate
limited functionality of the feature.
Every HTML element may have any number of custom data attributes specified, with any value.
Authors should carefully design such extensions so that when the attributes are ignored and any associated CSS dropped, the page is still usable.
User agents must not derive any implementation behavior from these attributes or values. Specifications intended for user agents must not define these attributes to have any meaningful values.
JavaScript libraries may use the custom data attributes, as they are considered to be part of the page on which they are used. Authors of libraries that are reused by many authors are encouraged to include their name in the attribute names, to reduce the risk of clashes. Where it makes sense, library authors are also encouraged to make the exact name used in the attribute names customizable, so that libraries whose authors unknowingly picked the same name can be used on the same page, and so that multiple versions of a particular library can be used on the same page even when those versions are not mutually compatible.
For example, a library called "DoQuery" could use attribute names like data-doquery-range, and a library called "jJo" could use attributes names like
data-jjo-range. The jJo library could also provide an API to set which
prefix to use (e.g. J.setDataPrefix('j2'), making the attributes have names
like data-j2-range).
datasetReturns a DOMStringMap object for the element's data-* attributes.
Hyphenated names become camel-cased. For example, data-foo-bar=""
becomes element.dataset.fooBar.
The dataset IDL attribute provides convenient
accessors for all the data-* attributes on an element. On
getting, the dataset IDL attribute must return a
DOMStringMap whose associated element is this element.
The DOMStringMap interface is used for the dataset attribute. Each DOMStringMap has an associated element.
[Exposed =Window ,
OverrideBuiltins ]
interface DOMStringMap {
getter DOMString (DOMString name );
[CEReactions ] setter void (DOMString name , DOMString value );
[CEReactions ] deleter void (DOMString name );
};To get a DOMStringMap's name-value
pairs, run the following algorithm:
Let list be an empty list of name-value pairs.
For each content attribute on the DOMStringMap's associated element whose first five characters are
the string "data-" and whose remaining characters (if any) do not include
any ASCII upper alphas, in the order that those
attributes are listed in the element's attribute list, add a name-value pair to
list whose name is the attribute's name with the first five characters removed and
whose value is the attribute's value.
For each name in list, for each U+002D HYPHEN-MINUS character (-) in the name that is followed by an ASCII lower alpha, remove the U+002D HYPHEN-MINUS character (-) and replace the character that followed it by the same character converted to ASCII uppercase.
Return list.
The supported property names on a DOMStringMap object at any instant
are the names of each pair returned from getting the
DOMStringMap's name-value pairs at that instant, in the order returned.
To determine the value of a named property
name for a DOMStringMap, return the value component of the name-value pair
whose name component is name in the list returned from getting the DOMStringMap's name-value
pairs.
To set the value of a new named property or
set the value of an existing named property for a DOMStringMap, given a
property name name and a new value value, run the following steps:
If name contains a U+002D HYPHEN-MINUS character (-) followed by an ASCII
lower alpha, then throw a "SyntaxError"
DOMException.
For each ASCII upper alpha in name, insert a U+002D HYPHEN-MINUS character (-) before the character and replace the character with the same character converted to ASCII lowercase.
Insert the string data- at the front of name.
If name does not match the XML Name production,
throw an "InvalidCharacterError" DOMException.
Set an attribute value for the
DOMStringMap's associated element
using name and value.
To delete an existing named property
name for a DOMStringMap, run the following steps:
For each ASCII upper alpha in name, insert a U+002D HYPHEN-MINUS character (-) before the character and replace the character with the same character converted to ASCII lowercase