This section is non-normative.
The World Wide Web's markup language has always been HTML. HTML was primarily designed as a language for semantically describing scientific documents, although its general design and adaptations over the years has enabled it to be used to describe a number of other types of documents.
The main area that has not been adequately addressed by HTML is a vague subject referred to as Web Applications. This specification attempts to rectify this, while at the same time updating the HTML specifications to address issues raised in the past few years.
This section is non-normative.
This specification is intended for authors of documents and scripts that use the features defined in this specification, and implementors of tools that are intended to conform to 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, readers should be familiar with the basics of DOM Core and DOM Events before reading this specification. An understanding of Web IDL, HTTP, XML, Unicode, character encodings, JavaScript, and CSS will 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 does not include documenting
every HTML or DOM feature supported by Web browsers. Browsers
support many features that are considered to be very bad for
accessibility or that are otherwise inappropriate. For example, the
blink element is clearly presentational and authors
wishing to cause text to blink should instead use CSS.
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. For instance 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.
Work on HTML 5 originally started in late 2003, as 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. 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.
In early 2004, some of the principles that underlie this effort, as well as an early draft proposal covering just forms-related features, were presented to the W3C jointly by Mozilla and Opera at a workshop discussing the future of Web Applications on the Web. The proposal was rejected on the grounds that the proposal conflicted with the previously chosen direction for the Web's evolution.
Shortly thereafter, Apple, Mozilla, and Opera jointly announced their intent to continue working on the effort. A public mailing list was created, and the drafts were moved to the WHATWG site. The copyright was subsequently amended to be jointly owned by all three vendors, and to allow reuse of the specifications.
In 2006, the W3C expressed interest in the specification, and created a working group chartered to work with the WHATWG on the development of the HTML 5 specifications. The working group opened in 2007. Apple, Mozilla, and Opera allowed the W3C to publish the specifications under the W3C copyright, while keeping versions with the less restrictive license on the WHATWG site.
Since then, both groups have been working together.
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 serialising the execution of all scripts in all browsing contexts.
The navigator.getStorageUpdates()
method, in this model, is equivalent to allowing other scripts to
run while the calling script is blocked.
This section is non-normative.
This specification interacts with and relies on a wide variety of other specifications. In certain circumstances, unfortunately, the desire to be compatible with legacy content has led to this specification violating the requirements of these other specifications. Whenever this has occurred, the transgressions have been noted as "willful violations".
This section is non-normative.
This specification describes a new revision of the HTML language and its associated DOM API.
The requirements in this specification for features that were already in HTML4 and DOM2 HTML are based primarily on the implementation and deployment experience collected over the past ten years. Some features have been removed from the language, based on best current practices; implementation requirements for some of these, as well as for non-standard features that have nonetheless garnered wide use, are still included in this specification to allow implementations to continue supporting legacy content. [HTML4] [DOM2HTML]
A separate document has been published by the W3C HTML working group to provide a more detailed reference of the differences between this specification and the language described in the HTML 4 specification. [HTMLDIFF]
This section is non-normative.
This specification is intended to replace XHTML 1.0 as the normative definition of the XML serialization of the HTML vocabulary. [XHTML10]
While this specification updates the semantics and requirements of the vocabulary defined by XHTML Modularization 1.1 and used by XHTML 1.1, it does not attempt to provide a replacement for the modularization scheme defined and used by those (and other) specifications, and therefore cannot be considered a complete replacement for them. [XHTMLMOD] [XHTML11]
Thus, authors and implementors who do not need such a modularization scheme can consider this specification a replacement for XHTML 1.x, but those who do need such a mechanism are encouraged to continue using the XHTML 1.1 line of specifications.
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 "DOM5 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 "HTML5". This is the format
recommended for most authors. It is compatible with all legacy Web
browsers. If a document is transmitted with the MIME type text/html, then it will be processed as an "HTML5"
document by Web browsers.
The second concrete syntax uses XML, and is known as
"XHTML5". When a document is transmitted with an XML MIME
type, such as application/xhtml+xml,
then it is processed by an XML processor by Web browsers, and
treated as an "XHTML5" document. Authors are reminded that the
processing for XML and HTML differs; in particular, even minor
syntax errors will prevent an XML document from being rendered
fully, whereas they would be ignored in the "HTML5" syntax.
The "DOM5 HTML", "HTML5", and "XHTML5" representations cannot all
represent the same content. For example, namespaces cannot be
represented using "HTML5", but they are supported in "DOM5 HTML" and
"XHTML5". Similarly, documents that use the noscript
feature can be represented using "HTML5", but cannot be represented
with "XHTML5" and "DOM5 HTML". Comments that contain the string
"-->" can be represented in "DOM5 HTML" but
not in "HTML5" and "XHTML5". And so forth.
This section is non-normative.
This specification is divided into the following major sections:
There are also a couple of appendices, defining rendering rules for Web browsers and listing areas that are out of scope for this specification.
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.
This is a definition, requirement, or explanation.
This is a note.
This is an example.
This is an open issue.
This is a warning.
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.
This is an implementation requirement.
This section is non-normative.
A basic HTML document looks like this:
<!DOCTYPE HTML> <html> <head> <title>Sample page</title> </head> <body> <h1>Sample page</h1> <p>This is a <a href="demo.html">simple</a> sample.</p> </body> </html>
HTML documents consist of a tree of elements and text. Each
element is denoted 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 correctly, so that elements do not partially overlap each other:
<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 above, 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 be left
unquoted if it is a keyword, but generally will be quoted. (The
value can also be omitted altogether if it is empty.)
The tree formed by an HTML document in this way is turned into a DOM tree when parsed. This DOM tree can then be manipulated from scripts. Since DOM trees are the "live" representation of an HTML document, this specification is mostly phrased in terms of DOM trees, instead of the serialisation described above.
Each element in the DOM tree is represented by an object, and
thus objects have APIs so that they can be manipulated. For
instance, a link can have its "href" attributed 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
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>
<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 may be difficult to understand at first.