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Abstract
This specification evolves HTML and its related APIs to ease the
authoring of Web-based applications. Additions include context
menus, a direct-mode graphics canvas, a full duplex client-server
communication channel, more semantics, audio and video, various
features for offline Web applications, sandboxed iframes, and scoped
styling. Heavy emphasis is placed on keeping the language backwards
compatible with existing legacy user agents and on keeping user
agents backwards compatible with existing legacy documents.
Status of this document
This is a work in progress! This document is
changing on a daily if not hourly basis in response to comments and
as a general part of its development process. Comments are very
welcome, please send them to whatwg@whatwg.org. Thank
you.
The current focus is in responding to the outstanding
feedback. (There is a chart showing
current progress.)
Implementors should be aware that this specification is not
stable. Implementors who are not taking part in the
discussions are likely to find the specification changing out from
under them in incompatible ways. Vendors interested in
implementing this specification before it eventually reaches the
call for implementations should join the WHATWG mailing list and take part in the
discussions.
This specification is also being produced by the W3C HTML WG. The two
specifications are identical from the table of contents onwards.
This specification is intended to replace (be the new version of)
what was previously the HTML4, XHTML 1.x, and DOM2 HTML
specifications.
Stability
Different parts of this specification are at different levels of
maturity.
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.
1.2 Audience
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.
1.3 Scope
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.
1.4 History
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.
1.5 Design notes
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.
1.5.1 Serializability of script execution
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.
1.5.2 Compliance with other specifications
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".
1.6 Relationships to other specifications
1.6.1 Relationship to HTML 4.01 and DOM2 HTML
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]
1.6.2 Relationship to XHTML 1.x
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.
1.7 HTML vs XHTML
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.
1.8 Structure of this specification
This section is non-normative.
This specification is divided into the following major
sections:
Documents are built from elements. These elements form a tree
using the DOM. This section defines the features of this DOM, as
well as introducing the features common to all elements, and the
concepts used in defining elements.
Each element has a predefined meaning, which is explained in
this section. Rules for authors on how to use the element, along with user agent requirements for how to handle
each element, are also given.
HTML documents do not exist in a vacuum — this section
defines many of the features that affect environments that deal
with multiple pages, links between pages, and running scripts.
Applications written in HTML often require mechanisms to
communicate with remote servers, as well as communicating with
other applications from different domains running on the same
client.
All of these features would be for naught if they couldn't be
represented in a serialized form and sent to other people, and so
this section defines the syntax of HTML, along with rules for how
to parse HTML.
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.
1.8.2 Typographic conventions
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
};
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.
1.9 A quick introduction to HTML
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.
2 Common infrastructure
2.1 Terminology
This specification refers to both HTML and XML attributes and DOM
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 DOM
attributes for those from the DOM. 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 XHTML 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 XHTML)".
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.
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.
When an algorithm B says to return to another algorithm A, it
implies that A called B. Upon returning to A, the implementation
must continue from where it left off in calling B.
2.1.1 XML
To ease migration from HTML to XHTML, 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 "elements in the HTML
namespace", or "HTML elements" for short, when used
in this specification, thus refers to both HTML and XHTML
elements.
Unless otherwise stated, all elements defined or mentioned in
this specification are in the
http://www.w3.org/1999/xhtml namespace, and all
attributes defined or mentioned in this specification have no
namespace (they are in the per-element partition).
When an XML name, such as an attribute or element name, is
referred to in the form prefix:localName, as in xml:id or
svg:rect, it refers to a name with the local name localName and the namespace given by the prefix, as
defined by the following table:
xml
http://www.w3.org/XML/1998/namespace
html
http://www.w3.org/1999/xhtml
svg
http://www.w3.org/2000/svg
Attribute names are said to be XML-compatible if they
match the Name production defined in XML, they contain no
U+003A COLON (:) characters, and their first three characters are
not an ASCII case-insensitive match for the string
"xml". [XML]
The term XML MIME type is used to refer to the MIME
types text/xml, application/xml, and any MIME type ending with the
four characters "+xml". [RFC3023]
2.1.2 DOM trees
The term root element, when not explicitly qualified
as referring to the document's root element, means the furthest
ancestor element node of whatever node is being discussed, or the
node itself if it has no ancestors. When the node is a part of the
document, then that is indeed the document's root element; however,
if the node is not currently part of the document tree, the root
element will be an orphaned node.
A node's home subtree is the subtree rooted at that
node's root element.
The Document of a Node (such as an
element) is the Document that the Node's
ownerDocument DOM attribute returns.
When an element's root element is the root
element of a Document, it is said to be in
a Document. An element is said to have been inserted into a
document when its root element changes and is now
the document's root element. Analogously, an element is
said to have been removed from a document when its root
element changes from being the document's root
element to being another element.
If a Node is in a Document
then that Document is always the Node's
Document, and the Node's ownerDocument DOM attribute thus always returns that
Document.
The term tree order means a pre-order, depth-first
traversal of DOM nodes involved (through the parentNode/childNodes
relationship).
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.
The term text node refers to any Text
node, including CDATASection nodes; specifically, any
Node with node type TEXT_NODE (3)
or CDATA_SECTION_NODE (4). [DOM3CORE]
A content attribute is said to change value
only if its value new value is different than its previous value;
setting an attribute to a value it already has does not change
it.
2.1.3 Scripting
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".
A DOM 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 that means
that any attributes returning that object must always return the same object (not a new
object each time), and the attributes and methods on that object
must operate on the actual underlying
data, not a snapshot of the data.
The terms fire and dispatch are used
interchangeably in the context of events, as in the DOM Events
specifications. [DOM3EVENTS]
2.1.4 Plugins
The term plugin is used to mean any content handler,
typically a third-party content handler, for Web content types that
are not supported by the user agent natively, or for content types
that do not expose a DOM, that supports rendering the content as
part of the user agent's interface.
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. [NPAPI]
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.
2.1.5 Character encodings
An ASCII-compatible character encoding is a
single-byte or variable-length encoding in which the bytes 0x09,
0x0A, 0x0C, 0x0D, 0x20 - 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A,
and 0x61 - 0x7A, ignoring bytes that
are the second and later bytes of multibyte sequences, all
correspond to single-byte sequences that map to the same Unicode
characters as those bytes in ANSI_X3.4-1968 (US-ASCII). [RFC1345]
This includes such encodings as Shift_JIS and
variants of ISO-2022, even though it is possible in this encodings
for bytes like 0x70 to be part of longer sequences that are
unrelated to their interpretation as ASCII. It excludes such
encodings as UTF-7, UTF-16, HZ-GB-2312, GSM03.38, and EBCDIC
variants.
2.1.6 Resources
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
actually also contained animation data.
A MPEG4 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.
2.2 Conformance requirements
All diagrams, examples, and notes in this specification are
non-normative, as are all sections explicitly marked non-normative.
Everything else in this specification is normative.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in the normative parts of this document are to be
interpreted as described in RFC2119. For readability, these words do
not appear in all uppercase letters in this specification. [RFC2119]
Requirements phrased in the imperative as part of
algorithms (such as "strip any leading space characters" or "return
false and abort these steps") are to be interpreted with the meaning
of the key word ("must", "should", "may", etc) used in introducing
the algorithm.
This specification describes the conformance criteria for user agents (relevant to implementors) and
documents (relevant to authors and authoring tool
implementors).
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 and other interactive user agents
Web browsers that support the XHTML 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 XHTML processor would, upon
finding an XHTML 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 as text/html 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 the Web IDL specification. [WEBIDL]
Non-interactive presentation user agents
User agents that process HTML and XHTML 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 with no scripting support
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
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 "HTML5 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:
Criteria that can be expressed in a DTD.
Criteria that cannot be expressed by a DTD, but can still be
checked by a machine.
Criteria that can only be checked by a human.
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.
Data mining tools
Applications and tools that process HTML and XHTML documents
for reasons other than to either render the documents or check
them for conformance should act in accordance to 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
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.
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 the author of the document or section. However, since an
authoring tool is likely unable to determine the difference, an
authoring tool is exempt from that requirement.
In terms of conformance checking, an editor is
therefore required 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.
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.
Conformance requirements phrased as algorithms or specific steps
may be implemented in any manner, so long as the end result is
equivalent. (In particular, the algorithms defined in this
specification are intended to be easy to follow, and not intended to
be performant.)
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
(referred to as the XHTML syntax), and one using a custom format inspired by SGML (referred to as
the HTML syntax). Implementations
may support only one of these two formats, although supporting both
is encouraged.
XML documents that use elements or
attributes from the HTML namespace and that are served
over the wire (e.g. by HTTP) must be sent using an XML MIME
type such as application/xml or
application/xhtml+xml and must not be served as
text/html. [RFC3023]
Documents that use the HTML
syntax, if they are served over the wire (e.g. by HTTP) must
be labeled with the text/html MIME type.
The language in this
specification assumes that the user agent expands all entity
references, and therefore does not include entity reference nodes in
the DOM. If user agents do include entity reference nodes in the
DOM, then user agents must handle them as if they were fully
expanded when implementing this specification. For example, if a
requirement talks about an element's child text nodes, then any text
nodes that are children of an entity reference that is a child of
that element would be used as well. Entity references to unknown
entities must be treated as if they contained just an empty text
node for the purposes of the algorithms defined in this
specification.
2.2.1 Dependencies
This specification relies on several other underlying
specifications.
XML
Implementations that support the XHTML syntax must
support some version of XML, as well as its corresponding
namespaces specification, because that syntax uses an XML
serialization with namespaces. [XML][XMLNAMES]
DOM
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.
[DOM3CORE]
Implementations must support some version of DOM Core and DOM
Events, because this specification is defined in terms of the DOM,
and some of the features are defined as extensions to the DOM Core
interfaces. [DOM3CORE][DOM3EVENTS]
Web IDL
The IDL fragments in this specification must be interpreted as
required for conforming IDL fragments, as described in the Web IDL
specification. [WEBIDL]
Unless otherwise specified, if a DOM attribute that is a
floating point number type (float) is
assigned an Infinity or Not-a-Number value, a
NOT_SUPPORTED_ERR exception must be raised.
Unless otherwise specified, if a method with an argument that
is a floating point number type (float) is
passed an Infinity or Not-a-Number value, a
NOT_SUPPORTED_ERR exception must be raised.
JavaScript
Some parts of the language described by this specification only
support JavaScript as the underlying scripting language. [ECMA262]
The term "JavaScript" is used to refer to ECMA262,
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]
Media Queries
Implementations must support some version of the Media Queries
language. [MQ]
This specification does not require support of any
particular network transport protocols, style sheet language,
scripting language, or any of the DOM and WebAPI specifications
beyond those described 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.
This specification might have certain additional
requirements on character encodings, image formats, audio formats,
and video formats in the respective sections.
2.2.2 Extensibility
Vendor-specific proprietary 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.
If markup extensions are needed, they should be done using XML,
with elements or attributes from custom namespaces. If DOM
extensions are needed, the members should be prefixed by
vendor-specific strings to prevent clashes with future versions of
this specification. Extensions must be defined so that the use of
extensions does not contradict nor cause the non-conformance of
functionality defined in the specification.
For example, while strongly discouraged to do so, an
implementation "Foo Browser" could add a new DOM attribute "fooTypeTime" to a control's DOM interface 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.
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.
2.3 Case-sensitivity and string comparison
This specification defines several comparison operators for
strings.
Comparing two strings in a case-sensitive manner means
comparing them exactly, code point for code point.
Comparing two strings in an ASCII case-insensitive
manner means comparing them exactly, code point for code point, except
that the characters in the range U+0041 .. U+005A (i.e. LATIN
CAPITAL LETTER A to LATIN CAPITAL LETTER Z) and the corresponding
characters in the range U+0061 .. U+007A (i.e. LATIN SMALL LETTER A
to LATIN SMALL LETTER Z) are considered to also match.
Comparing two strings in a compatibility caseless
manner means using the Unicode compatibility caseless match
operation to compare the two strings. [UNICODECASE]
Converting a string to
ASCII uppercase means replacing all characters in the range
U+0061 .. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z)
with the corresponding characters in the range U+0041 .. U+005A
(i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).
Converting a string to
ASCII lowercase means replacing all characters in the range
U+0041 .. U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL
LETTER Z) with the corresponding characters in the range U+0061
.. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z).
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.
2.4 Common microsyntaxes
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.
2.4.1 Common parser idioms
The space characters, for the
purposes of this specification, are U+0020 SPACE, U+0009 CHARACTER
TABULATION (tab), U+000A LINE FEED (LF), U+000C FORM FEED (FF), and
U+000D CARRIAGE RETURN (CR).
The White_Space characters are
those that have the Unicode property "White_Space". [UNICODE]
The alphanumeric ASCII characters are those in the
ranges U+0030 DIGIT ZERO .. U+0039 DIGIT NINE, U+0041 LATIN CAPITAL
LETTER A .. U+005A LATIN CAPITAL LETTER Z, U+0061 LATIN SMALL LETTER
A .. U+007A LATIN SMALL LETTER Z.
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.
For parsers based on this pattern, a step that requires the user
agent to collect a sequence of characters means that the
following algorithm must be run, with characters
being the set of characters that can be collected:
Let input and position be the same variables as those of the same
name in the algorithm that invoked these steps.
Let result be the empty string.
While position doesn't point past the
end of input and the character at position is one of the characters, append that character to the end of result and advance position to
the next character in input.
When a user agent is to strip line breaks from a
string, the user agent must remove any U+000A LINE FEED (LF) and
U+000D CARRIAGE RETURN (CR) characters from that string.
The code-point length of a string is the number of
Unicode code points in that string.
2.4.2 Boolean attributes
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.
2.4.3 Keywords and enumerated attributes
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, if the attribute value matches
none of the keywords but there is a missing value default
state defined, then that is the state represented by the
attribute. Otherwise, there is no default, and invalid values must
be ignored.
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.
2.4.4 Numbers
2.4.4.1 Non-negative integers
A string is a valid non-negative integer if it
consists of one or more characters in the range U+0030 DIGIT ZERO
(0) to U+0039 DIGIT NINE (9).
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 either return zero, a positive integer,
or an error. Leading spaces are ignored. Trailing spaces and any
trailing garbage characters are ignored.
Let input be the string being
parsed.
Let position be a pointer into input, initially pointing at the start of the
string.
If position is past the end of input, return an error.
If the next character is a U+002B PLUS SIGN character (+),
advance position to the next character.
If position is past the end of input, return an error.
If the next character is not one of U+0030 DIGIT ZERO (0)
.. U+0039 DIGIT NINE (9), then return an error.
Loop: If the next character is one of U+0030 DIGIT ZERO
(0) .. U+0039 DIGIT NINE (9):
Multiply value by ten.
Add the value of the current character (0..9) to value.
Advance position to the next
character.
If position is not past the end of input, return to the top of the step labeled
loop in the overall algorithm (that's the step within
which these substeps find themselves).
Return value.
2.4.4.2 Signed integers
A string is a valid integer if it consists of one or
more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT
NINE (9), 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 integerwith 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 similar to the
rules for
non-negative integers, and 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 either return an integer or an error. Leading spaces
are ignored. Trailing spaces and trailing garbage characters are
ignored.
Let input be the string being
parsed.
Let position be a pointer into input, initially pointing at the start of the
string.
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:
Let sign be "negative".
Advance position to the next
character.
If position is past the end of input, return an error.
If the next character is not one of U+0030 DIGIT ZERO (0)
.. U+0039 DIGIT NINE (9), then return an error.
If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039
DIGIT NINE (9):
Multiply value by ten.
Add the value of the current character (0..9) to value.
Advance position to the next
character.
If position is not past the end of input, return to the top of step 9 in the overall
algorithm (that's the step within which these substeps find
themselves).
If sign is "positive", return value, otherwise return 0-value.
2.4.4.3 Real numbers
A string is a valid floating point number if it
consists of:
Optionally, a U+002D HYPHEN-MINUS ("-") character.
A series of one or more characters in the range U+0030 DIGIT
ZERO (0) to U+0039 DIGIT NINE (9).
Optionally:
A single U+002E FULL STOP (".") character.
A series of one or more characters in the range U+0030 DIGIT
ZERO (0) to U+0039 DIGIT NINE (9).
Optionally:
Either a U+0065 LATIN SMALL LETTER E character or a U+0045
LATIN CAPITAL LETTER E character.
Optionally, a U+002D HYPHEN-MINUS ("-") character or U+002B
PLUS SIGN ("+") character.
A series of one or more characters in the range U+0030 DIGIT
ZERO (0) to U+0039 DIGIT NINE (9).
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 best representation of the floating point number
n is the string obtained from applying the
JavaScript operator ToString to n.
The rules for parsing floating point number values are
as given in the following algorithm. As with the previous
algorithms, when this one is invoked, the steps must be followed in
the order given, aborting at the first step that returns
something. This algorithm will either return a number or an
error. Leading spaces are ignored. Trailing spaces and garbage
characters are ignored.
Let input be the string being
parsed.
Let position be a pointer into input, initially pointing at the start of the
string.
If position is past the end of input, return an error.
If the character indicated by position is a
U+002D HYPHEN-MINUS ("-") character:
Change value and divisor to −1.
Advance position to the next
character.
If position is past the end of input, return an error.
If the character indicated by position
is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then
return an error.
Collect a sequence of characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and interpret the
resulting sequence as a base-ten integer. Multiply value by that integer.
If position is past the end of input, return value.
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 one of U+0030 DIGIT ZERO (0)
.. U+0039 DIGIT NINE (9), then return value.
Fraction loop: Multiply divisor
by ten.
Add the value of the current character interpreted as a
base-ten digit (0..9) divided by divisor, to
value.
Advance position to the next
character.
If position is past the end of input, then return value.
If the character indicated by position
is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), return
to the step labeled fraction loop in these
substeps.
If the character indicated by position
is a U+0065 LATIN SMALL LETTER E character or a U+0045 LATIN
CAPITAL LETTER E character, run these substeps:
Advance position to the next
character.
If position is past the end of input, then return value.
If the character indicated by position is
a U+002D HYPHEN-MINUS ("-") character:
Change exponent to −1.
Advance position to the next
character.
If position is past the end of input, then return value.
Otherwise, if the character indicated by position is a U+002B PLUS SIGN ("+")
character:
Advance position to the next
character.
If position is past the end of input, then return value.
If the character indicated by position
is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9),
then return value.
Collect a sequence of characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and interpret the
resulting sequence as a base-ten integer. Multiply exponent by that integer.
Multiply value by ten raised to the
exponentth power.
Return value.
2.4.4.4 Ratios
The algorithms described in this section are used by
the progress and meter elements.
A valid denominator punctuation character is one of
the characters from the table below. There is a value
associated with each denominator punctuation character, as
shown in the table below.
Denominator Punctuation Character
Value
U+0025 PERCENT SIGN
%
100
U+066A ARABIC PERCENT SIGN
٪
100
U+FE6A SMALL PERCENT SIGN
﹪
100
U+FF05 FULLWIDTH PERCENT SIGN
％
100
U+2030 PER MILLE SIGN
‰
1000
U+2031 PER TEN THOUSAND SIGN
‱
10000
The steps for finding one or two numbers of a ratio in a
string are as follows:
If the string is empty, then return nothing and abort these
steps.
Find a number in the string according to the
algorithm below, starting at the start of the string.
If the sub-algorithm in step 2 returned nothing or returned an
error condition, return nothing and abort these steps.
Set number1 to the number returned by the
sub-algorithm in step 2.
Starting with the character immediately after the last one
examined by the sub-algorithm in step 2, skip all
White_Space characters in the string (this might match
zero characters).
If there are still further characters in the string, and the
next character in the string is a valid denominator
punctuation character, set denominator
to that character.
If the string contains any other characters in the range U+0030
DIGIT ZERO to U+0039 DIGIT NINE, but denominator was
given a value in the step 6, return nothing and abort these
steps.
Otherwise, if denominator was given a value
in step 6, return number1 and denominator and abort these steps.
Find a number in the string again, starting
immediately after the last character that was examined by the
sub-algorithm in step 2.
If the sub-algorithm in step 9 returned nothing or an error
condition, return number1 and abort these
steps.
Set number2 to the number returned by the
sub-algorithm in step 9.
Starting with the character immediately after the last one
examined by the sub-algorithm in step 9, skip all
White_Space characters in the string (this might match
zero characters).
If there are still further characters in the string, and the
next character in the string is a valid denominator
punctuation character, return nothing and abort these
steps.
If the string contains any other characters in the range U+0030
DIGIT ZERO to U+0039 DIGIT NINE, return nothing and abort these
steps.
Otherwise, return number1 and
number2.
The algorithm to find a number is as follows. It is
given a string and a starting position, and returns either nothing,
a number, or an error condition.
Starting at the given starting position, ignore all characters
in the given string until the first character that is either a
U+002E FULL STOP or one of the ten characters in the range U+0030
DIGIT ZERO to U+0039 DIGIT NINE.
If there are no such characters, return nothing and abort these
steps.
Starting with the character matched in step 1, collect all the
consecutive characters that are either a U+002E FULL STOP or one of
the ten characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT
NINE, and assign this string of one or more characters to
string.
If string consists of just a single U+002E
FULL STOP character or if it contains more than one U+002E FULL
STOP character then return an error condition and abort these
steps.
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 either return a number greater than or
equal to 1.0, 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 position be a pointer into input, initially pointing at the start of the
string.
If position is past the end of input, return an error.
If the next character is not one of U+0031 DIGIT ONE (1)
.. U+0039 DIGIT NINE (9), then return an error.
Collect a sequence of characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), and interpret the
resulting sequence as a base-ten integer. Let value be that number.
If position is past the end of input, return value as an
integer.
If the next character is a U+002E FULL STOP character (.):
Advance position to the next
character.
If the next character is not one of U+0030 DIGIT ZERO (0)
.. U+0039 DIGIT NINE (9), then return value
as an integer.
Collect a sequence of characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). Let length be the number of characters collected. Let
fraction be the result of interpreting the
collected characters as a base-ten integer, and then dividing
that number by 10length.
Increment value by fraction.
If position is past the end of input, return value as a
length.
If the next character is a U+0025 PERCENT SIGN character
(%), return value as a percentage.
Return value as a length.
2.4.4.6 Lists of integers
A valid list of integers is a number of valid integers separated by U+002C
COMMA characters, with no other characters (e.g. no space characters). In addition, there
might be restrictions on the number of integers that can be given,
or on the range of values allowed.
The rules for parsing a list of integers 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 integers. This list will be the result of this
algorithm.
If there is a character in the string input at position position, and
it is either a U+0020 SPACE, U+002C COMMA, or U+003B SEMICOLON
character, then advance position to the next
character in input, or to beyond the end of the
string if there are no more characters.
If position points to beyond the end of
input, return numbers and
abort.
If the character in the string input at
position position is a U+0020 SPACE, U+002C
COMMA, or U+003B SEMICOLON character, then return to step 4.
Let negated be false.
Let value be 0.
Let started be false. This variable is
set to true when the parser sees a number or a U+002D HYPHEN-MINUS
("-") character.
Let got number be false. This variable
is set to true when the parser sees a number.
Let finished be false. This variable is
set to true to switch parser into a mode where it ignores
characters until the next separator.
Let bogus be false.
Parser: If the character in the string input at position position
is:
A U+002D HYPHEN-MINUS character
Follow these substeps:
If got number is true, let finished be true.
If finished is true, skip to the next
step in the overall set of steps.
If started is true, let negated be false.
Otherwise, if started is false and if bogus is false, let negated
be true.
Let started be true.
A character in the range U+0030 DIGIT ZERO .. U+0039 DIGIT
NINE
Follow these substeps:
If finished is true, skip to the next
step in the overall set of steps.
Multiply value by ten.
Add the value of the digit, interpreted in base ten, to
value.
Let started be true.
Let got number be true.
A U+0020 SPACE character
A U+002C COMMA character
A U+003B SEMICOLON character
Follow these substeps:
If got number is false, return the numbers list and abort. This happens if an entry
in the list has no digits, as in "1,2,x,4".
If negated is true, then negate value.
Append value to the numbers list.
Jump to step 4 in the overall set of steps.
A character in the range U+0001 .. U+001F, U+0021 .. U+002B, U+002D .. U+002F, U+003A, U+003C .. U+0040, U+005B .. U+0060, U+007b .. U+007F
(i.e. any other non-alphabetic ASCII character)
Follow these substeps:
If got number is true, let finished be true.
If finished is true, skip to the next
step in the overall set of steps.
Let negated be false.
Any other character
Follow these substeps:
If finished is true, skip to the next
step in the overall set of steps.
Let negated be false.
Let bogus be true.
If started is true, then return the
numbers list, and abort. (The value in value is not appended to the list first; it is
dropped.)
Advance position to the next character
in input, or to beyond the end of the string if
there are no more characters.
If position points to a character (and
not to beyond the end of input), jump to the
big Parser step above.
If negated is true, then negate value.
If got number is true, then append value to the numbers list.
Return the numbers list and
abort.
2.4.4.7 Lists of dimensions
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.
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 a
character in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE
(9), collect a sequence of characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), interpret the
resulting sequence as an integer in base ten, and increment value by that integer.
If the character at position is a U+002E
FULL STOP character (.), run these substeps:
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.
2.4.5 Dates and times
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]
The digits in the date
and time syntaxes defined in this section must be characters in the
range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, used to express
numbers in base ten.
2.4.5.1 Months
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:
Four or more digits, representing year, where year > 0
A U+002D HYPHEN-MINUS character (-)
Two digits,
representing the month month, in the range
1 ≤ month ≤ 12
The rules to parse a month string are as follows. This
will either return 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.
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 either return 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 characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). 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 characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). 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.
2.4.5.2 Dates
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 either return 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 either return 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.
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 characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). 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 ≤ month ≤ maxday, then fail.
Return year, month,
and day.
2.4.5.3 Times
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:
Two digits,
representing hour, in the range
0 ≤ hour ≤ 23
A U+003A COLON character (:)
Two digits,
representing minute, in the range
0 ≤ minute ≤ 59
Optionally (required if second is
non-zero):
A U+003A COLON character (:)
Two digits,
representing the integer part of second, in
the range 0 ≤ s ≤ 59
Optionally (required if second is not an
integer):
A 002E FULL STOP character (.)
One or more digits, representing the
fractional part of second
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 either return 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 either return 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 characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). 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 hour is not a number in the range
0 ≤ hour ≤ 23, then
fail.
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 characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). 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.
If minute is not a number in the range
0 ≤ minute ≤ 59, then
fail.
Let second be a string with the value
"0".
If position is not beyond the end of
input and the character at position is a U+003A COLON, then run these
substeps:
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 two characters both in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then
fail.
Collect a sequence of characters that are
either characters in the range U+0030 DIGIT ZERO (0) to U+0039
DIGIT NINE (9) or U+002E FULL STOP characters. If the collected
sequence has more than one U+002E FULL STOP characters, or if the
last character in the sequence is a U+002E FULL STOP character,
then fail. Otherwise, let the collected string be second instead of its previous value.
Interpret second as a base-ten number
(possibly with a fractional part). Let second
be that number instead of the string version.
If second is not a number in the range
0 ≤ second < 60, then
fail.
Return hour, minute,
and second.
2.4.5.4 Local dates and times
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:
The rules to parse a local date and time string are as
follows. This will either return 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 not a U+0054 LATIN CAPITAL LETTER T
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.
2.4.5.5 Global dates and times
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, consisting of a 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:
A U+005A LATIN CAPITAL LETTER Z character, allowed only if
the time zone is UTC
Or:
Either a U+002B PLUS SIGN character (+) or a U+002D
HYPHEN-MINUS (-) character, representing the sign of the
time-zone offset
Two digits,
representing the hours component hour of
the time-zone offset, in the range 0 ≤ hour ≤ 23
A U+003A COLON character (:)
Two digits,
representing the minutes component minute
of the time-zone offset, in the range 0 ≤ minute ≤ 59
This format allows for time zone offsets from -23:59
to +23:59. In practice, however, the range of actual time zones is
-12:00 to +14:00, and the minutes component of actual time zones is
always either 00, 30, or 45.
Midnight UTC on the birthday of Nero (the Roman Emperor).
"1979-10-14T12:00:00.001-04:00"
One millisecond after noon on October 14th 1979, in the time
zone in use on the east coast of North America during daylight
saving time.
"8592-01-01T02:09+02:09"
Midnight UTC on the 1st of January, 8592. The time zone
associated with that time is two hours and nine minutes ahead of
UTC, which is not a real time zone currently, but is nonetheless
allowed.
Several things are notable about these dates:
Years with fewer than four digits have to be
zero-padded. The date "37-12-13" would not be a valid date.
To unambiguously identify a moment in time prior to the
introduction of the Gregorian calendar, the date has to be first
converted to the Gregorian calendar from the calendar in use at
the time (e.g. from the Julian calendar). The date of Nero's birth
is the 15th of December 37, in the Julian Calendar, which is the
13th of December 37 in the proleptic Gregorian Calendar.
The time and time-zone components are not optional.
Dates before the year zero can't be represented as a datetime
in this version of HTML.
Time zones differ based on daylight savings time.
The rules to parse a global date and time string are
as follows. This will either return a time in UTC, with associated
time-zone 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 not a U+0054 LATIN CAPITAL LETTER T
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 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.
The rules to parse a time-zone component, given an input string and a position, are
as follows. This will either return 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, 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 characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). 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 timezonehours.
If timezonehours is
not a number in the range 0 ≤ timezonehours ≤ 23, then fail.
If sign is "negative", then negate 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 characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). 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 timezoneminutes is
not a number in the range 0 ≤ timezoneminutes ≤ 59, then fail.
If sign is "negative", then negate timezoneminutes.
Return timezonehours
and timezoneminutes.
2.4.5.6 Weeks
A week consists of a week-year
number and a week number representing a seven day period. Each
week-year in this calendaring system has either 52 weeks or 53
weeks, as defined below. A week is a seven-day period. The week
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.
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:
Four or more digits, representing year, where year > 0
A U+002D HYPHEN-MINUS character (-)
A U+0057 LATIN CAPITAL LETTER W character
Two digits,
representing the week week, in the range
1 ≤ week ≤ maxweek, where maxweek is the
week number of the last day of week-year year
The rules to parse a week string are as follows. This
will either return 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 characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). 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, then fail. Otherwise, move position
forwards one character.
Collect a sequence of characters in the range
U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). 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.
A string is a valid date or time string in content if
it consists of zero or more White_Space characters,
followed by a valid date or time string, followed by
zero or more further White_Space characters.
The rules to parse a date or time string are as
follows. The algorithm is invoked with a flag indicating if the
in attribute variant or the in content variant is to
be used. The algorithm will either return 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 a U+0054 LATIN CAPITAL LETTER T
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 not a U+0054 LATIN CAPITAL LETTER T
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 set the time present flag to false.
If both the date present and time present flags are false, then fail.
If the time present flag is 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 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.
2.4.6 Colors
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 in the
range U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), U+0041 LATIN
CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, U+0061 LATIN
SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, 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 .. 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 either return 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 in the range U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE
(9), U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER
F, U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, then
return an error.
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 the digits U+0030 DIGIT ZERO
(0) .. U+0039 DIGIT NINE (9) and U+0061 LATIN SMALL LETTER A
.. U+0066 LATIN SMALL LETTER F, zero-padding if necessary, and
append these numbers to result, in the order
red, green, blue.
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 either
return a simple color or an error.
Let input be the string being
parsed.
If input is the empty string, then
return an error.
If input is an ASCII
case-insensitive match for the string "transparent", then return an error.
If input is four characters long, and the
first character in input is a U+0023 NUMBER
SIGN (#) character, and the last three characters of input are all in the range U+0030 DIGIT ZERO (0)
.. U+0039 DIGIT NINE (9), U+0041 LATIN CAPITAL LETTER A .. U+0046
LATIN CAPITAL LETTER F, and U+0061 LATIN SMALL LETTER A .. U+0066
LATIN SMALL LETTER F, then run these substeps:
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 Unicode 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 in the range U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9),
U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, and
U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F 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.
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.
2.4.7 Space-separated tokens
A set of space-separated tokens is a set of zero or
more words separated by one or more space characters, where words consist of any
string of one or more characters, none of which are space characters.
An unordered set of unique space-separated tokens is a
set of space-separated tokens where none of the words
are duplicated.
An ordered set of unique space-separated tokens is a
set of space-separated tokens where none of the words
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.
When a user agent has to split a string on spaces, it
must use the following algorithm:
Let input be the string being
parsed.
Let position be a pointer into input, initially pointing at the start of the
string.
If position is not past the end of
input, and output is not
the empty string, append a single U+0020 SPACE character at the
end of output.
Otherwise, append s to the end of output.
Return to step 6 in the overall set of steps.
This causes any occurrences of the token to be
removed from the string, and any spaces that were surrounding the
token to be collapsed to a single space, except at the start and end
of the string, where such spaces are removed.
2.4.8 Comma-separated tokens
A set of comma-separated tokens is a set of 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
space characters, nor
containing any U+002C COMMA characters (,),
and optionally surrounded by space
characters.
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.
When a user agent has to split a string on commas, it
must use the following algorithm:
Let input be the string being
parsed.
Let position be a pointer into input, initially pointing at the start of the
string.
Let tokens be a list of tokens,
initially empty.
Token: If position is past the
end of input, jump to the last step.
Collect a sequence of characters that are not
U+002C COMMA characters (,). Let s be the resulting sequence (which might be the
empty string).
Remove any leading or trailing sequence of space characters from s.
Add s to tokens.
If position is not past the end of input, then the character at position is a U+002C COMMA character (,); advance position past that
character.
Jump back to the step labeled token.
Return tokens.
2.4.9 Reversed DNS identifiers
A valid reversed DNS identifier is a string that
consists of a series of IDNA labels in reverse order (i.e. starting
with the top-level domain), the prefix of which, when reversed and
converted to ASCII, corresponds to a registered domain.
For instance, the string "com.example.xn--74h" is a valid reversed DNS
identifier because the string "example.com" is a registered domain.
Apply the IDNA ToASCII algorithm to the string, with both the
AllowUnassigned and UseSTD3ASCIIRules flags set, but between steps
2 and 3 of the general ToASCII/ToUnicode algorithm (i.e. after
splitting the domain name into individual labels), reverse the
order of the labels.
If ToASCII fails to convert one of the components of the
string, e.g. because it is too long or because it contains invalid
characters, then the string is not valid; abort these steps. [RFC3490]
Check that the end of the resulting string matches a suffix in
the Public Suffix List, and that there is at least one domain
label before the matching substring. If it does not, or if there
is not, then the string is not valid; abort these steps. [PSL]
Check that the domain name up to the label before the prefix
that was matched in the previous string is a registered domain
name.
2.4.10 References
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 in the document with type type.
The rules for parsing a hash-name reference to an
element of type type 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 and abort these
steps.
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
that has an id attribute whose value
is a case-sensitive match for s or
a name attribute whose value is a
compatibility caseless match for s.
2.5 URLs
2.5.1 Terminology
A URL is a string used to identify a resource.
A URL is a valid URL if it is a
valid Web address as defined by the Web addresses
specification. [WEBADDRESSES]
A URL is an absolute URL if it is an
absolute Web address as defined by the Web addresses
specification. [WEBADDRESSES]
To parse a URL url into its
component parts, the user agent must use the parse a Web
address algorithm defined by the Web addresses
specification. [WEBADDRESSES]
Parsing a URL results in the following components, again as
defined by the Web addresses specification:
<scheme>
<host>
<port>
<hostport>
<path>
<query>
<fragment>
<host-specific>
To resolve a URL to an absolute URL
relative to either another absolute URL or an element,
the user agent must use the resolve a Web address
algorithm defined by the Web addresses specification. [WEBADDRESSES]
The document base URL of a Document
object is the document base Web address as defined by
the Web addresses specification. [WEBADDRESSES]
The term "URL" in this specification is used in a
manner distinct from the precise technical meaning it is given in
RFC 3986. Readers familiar with that RFC will find it easier to read
this specification if they pretend the term "URL" as used
herein is really called something else altogether. This is a
willful violation of RFC 3986. [RFC3986]
When an element is moved from one document to another, if the two
documents have different base
URLs, then that element and all its descendants are
affected by a base URL change.
When an element is affected by a base URL change, it
must act as described in the following list:
If the absolute 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 re-resolved relative to the element
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 absolute URL(s) are being shown to the
user, then the ping
attribute's tokens should be re-resolved relative to the element and the UI updated
appropriately.
If the absolute 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 re-resolved relative to the element and the UI updated
appropriately.
Otherwise
The element is not directly affected.
Changing the base URL doesn't affect the image
displayed by img elements, although subsequent
accesses of the src DOM attribute
from script will return a new absolute URL that might
no longer correspond to the image being shown.
2.5.3 Interfaces for URL manipulation
An interface that has a complement of URL decomposition
attributes will have seven attributes with the following
definitions:
Returns the current fragment identifier in the underlying URL.
Can be set, to change the underlying URL's fragment identifier.
The attributes defined to be URL decomposition attributes must
act as described for the attributes with the same corresponding
names in this section.
In addition, an interface with a complement of URL decomposition
attributes will define an input, which is a URL
that the attributes act on, and a common setter action, which is a
set of steps invoked when any of the attributes' setters are
invoked.
The seven URL decomposition attributes have similar
requirements.
On getting, if the input
is an absolute URL that fulfills the condition given in
the "getter condition" column corresponding to the attribute in the
table below, the user agent must return the part of the input URL given in the "component"
column, with any prefixes specified in the "prefix" column
appropriately added to the start of the string and any suffixes
specified in the "suffix" column appropriately added to the end of
the string. Otherwise, the attribute must return the empty
string.
On setting, the new value must first be mutated as described by
the "setter preprocessor" column, then mutated by %-escaping any
characters in the new value that are not valid in the relevant
component as given by the "component" column. Then, if the input is an absolute
URL and the resulting new value fulfills the condition given
in the "setter condition" column, the user agent must make a new
string output by replacing the component of the
URL given by the "component" column in the input URL with the new value;
otherwise, the user agent must let output be
equal to the input. Finally,
the user agent must invoke the common setter action with the
value of output.
When replacing a component in the URL, if the component is part
of an optional group in the URL syntax consisting of a character
followed by the component, the component (including its prefix
character) must be included even if the new value is the empty
string.
The previous paragraph applies in particular to the
":" before a <port> component, the "?" before a <query> component, and the "#" before a <fragment> component.
For the purposes of the above definitions, URLs must be parsed
using the URL parsing rules defined
in this specification.
input is hierarchical, uses a server-based naming authority, and contained a <port> component (possibly an empty one)
—
—
Remove any characters in the new value that are not in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE.
If the resulting string is empty, set it to a single U+0030 DIGIT ZERO character ('0').
input is hierarchical and uses a server-based naming authority
The (empty) <fragment> component is not part of the <query> component.
2.6 Fetching resources
When a user agent is to fetch a resource, the
following steps must be run:
If the resource is identified by the URLabout:blank, then return the empty string
and abort these steps.
Perform the remaining steps asynchronously.
If the resource is identified by an absolute URL,
and the resource is to be obtained using a idempotent action (such
as an HTTP GET or
equivalent), and it is already being downloaded for other
reasons (e.g. another invocation of this algorithm), and the user
agent is configured such that it is to reuse the data from the
existing download instead of initiating a new one, then use the
results of the existing download instead of starting a new
one.
Otherwise, at a time convenient to the user and the user agent,
download (or otherwise obtain) the resource, applying the
semantics of the relevant specifications (e.g. performing an HTTP
GET or POST operation, or reading the file from disk, following
redirects, dereferencing javascript:
URLs, etc).
For purposes of generating the address of the resource from
which Request-URIs are obtained as required by HTTP for the
Referer (sic) header, the user
agent must use the document's current address of the
appropriate Document as given by this list. [HTTP]
Release the storage mutex so that it is once
again free.
When the resource is available, or if there is an error of
some description, queue a task that uses the resource
as appropriate. If the resource can be processed incrementally, as,
for instance, with a progressively interlaced JPEG or an HTML file,
additional tasks may be queued to process the data as it is
downloaded. The task source for these tasks is the
networking task source.
The navigation
processing model handles redirects itself, overriding the
redirection handling that would be done by the fetching
algorithm.
Whether the type
sniffing rules apply to the fetched resource depends on the
algorithm that invokes the rules — they are not always
applicable.
2.6.1 Protocol concepts
User agents can implement a variety of transfer protocols, but
this specification mostly defines behavior in terms of HTTP. [HTTP]
The HTTP GET
method is equivalent to the default retrieval action of the
protocol. For example, RETR in FTP. Such actions are idempotent and
safe, in HTTP terms.
The HTTP response
codes are equivalent to statuses in other protocols that have
the same basic meanings. For example, a "file not found" error is
equivalent to a 404 code, a server error is equivalent to a 5xx
code, and so on.
The HTTP
headers are equivalent to fields in other protocols that have
the same basic meaning. For example, the HTTP authentication
headers are equivalent to the authentication aspects of the FTP
protocol.
2.6.2 Encrypted HTTP and related security concerns
Anything in this specification that refers to HTTP also applies
to HTTP-over-TLS, as represented by URLs
representing the https scheme.
User agents should report certificate errors to
the user and must either refuse to download resources sent with
erroneous certificates or must act as if such resources were in fact
served with no encryption.
Not doing so can result in users not noticing man-in-the-middle
attacks.
If a user connects to a server with a self-signed certificate,
the user agent could allow the connection but just act as if there
had been no encryption. If the user agent instead allowed the user
to override the problem and then displayed the page as if it was
fully and safely encrypted, the user could be easily tricked into
accepting man-in-the-middle connections.
If a user connects to a server with full encryption, but the
page then refers to an external resource that has an expired
certificate, then the user agent will act as if the resource was
unavailable, possibly also reporting the problem to the user. If
the user agent instead allowed the resource to be used, then an
attacker could just look for "secure" sites that used resources
from a different host and only apply man-in-the-middle attacks to
that host, for example taking over scripts in the page.
2.6.3 Determining the type of a resource
The Content-Type metadata of a
resource must be obtained and interpreted in a manner consistent
with the requirements of the Content-Type Processing Model
specification. [MIMESNIFF]
The algorithm for extracting an encoding from a
Content-Type, given a string s, is given
in the Content-Type Processing Model specification. It either
returns an encoding or nothing. [MIMESNIFF]
The sniffed type of a
resource must be found in a manner consistent with the
requirements given in the Content-Type Processing Model
specification for finding that sniffed type. [MIMESNIFF]
The rules for sniffing
images specifically are also defined in the Content-Type
Processing Model specification. [MIMESNIFF]
It is imperative that the rules in the
Content-Type Processing Model specification 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 the Content-Type Processing Model
specification. [MIMESNIFF]
2.7 Character encodings
User agents must at a minimum support the UTF-8 and Windows-1252
encodings, but may support more.
It is not unusual for Web browsers to support dozens
if not upwards of a hundred distinct character encodings.
User agents must support the preferred MIME name of every
character encoding they support that has a preferred MIME name, and
should support all the IANA-registered aliases. [IANACHARSET]
When comparing a string specifying a character encoding with the
name or alias of a character encoding to determine if they are
equal, user agents must use the Charset Alias Matching rules defined
in Unicode Technical Standard #22. [UTS22]
For instance, "GB_2312-80" and "g.b.2312(80)" are
considered equivalent names.
When a user agent would otherwise use an encoding specified by a
label given in the first column of the following table to either
convert content to Unicode characters or convert Unicode characters
to bytes, it must instead use the encoding given in the cell in the
second column of the same row. When a byte or sequence of bytes is
treated differently due to this encoding aliasing, it is said to
have been misinterpreted for compatibility.
The requirement to treat certain encodings as other
encodings according to the table above is a willful
violation of the W3C Character Model specification, motivated
by a desire for compatibility with legacy content. [CHARMOD]
Support for encodings based on EBCDIC is not recommended. This
encoding is rarely used for publicly-facing Web content.
Support for UTF-32 is not recommended. This encoding is rarely
used, and frequently implemented incorrectly.
This specification does not make any attempt to
support EBCDIC-based encodings and UTF-32 in its algorithms; support
and use of these encodings can thus lead to unexpected behavior in
implementations of this specification.
2.8 Common DOM interfaces
2.8.1 Reflecting content attributes in DOM attributes
Some DOM attributes are
defined to reflect a particular content
attribute. This means that on getting, the DOM attribute
returns the current value of the content attribute, and on setting,
the DOM attribute changes the value of the content attribute to the
given value.
A list of reflecting DOM attributes and
their corresponding content attributes is given in the index.
In general, on getting, if the content attribute is not present,
the DOM 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 DOM attribute is a DOMString
attribute whose content attribute is defined to contain a
URL, then on getting, the DOM attribute must resolve the value of the content
attribute relative to the element and return the resulting
absolute URL if that was successful, or the empty
string otherwise; and on setting, must set the content attribute to
the specified literal value. If the content attribute is absent, the
DOM attribute must return the default value, if the content
attribute has one, or else the empty string.
If a reflecting DOM attribute is a DOMString
attribute whose content attribute is defined to contain one or more
URLs, then on getting, the DOM attribute
must split the content
attribute on spaces and return the concatenation of resolving each token URL to an
absolute URL relative to the element, with a single
U+0020 SPACE character between each URL, ignoring any tokens that
did not resolve successfully. If the content attribute is absent,
the DOM attribute must return the default value, if the content
attribute has one, or else the empty string. On setting, the DOM
attribute must set the content attribute to the specified literal
value.
If a reflecting DOM attribute is a DOMString whose
content attribute is an enumerated attribute, and the
DOM attribute is limited to only known values, then, on
getting, the DOM attribute must return the conforming value
associated with the state the attribute is in (in its canonical
case), or the empty string if the attribute is in a state that has
no associated keyword value; and on setting, if the new value is an
ASCII case-insensitive match for one of the keywords
given for that attribute, then the content attribute must be set to
the conforming value associated with the state that the attribute
would be in if set to the given new value, otherwise, if the new
value is the empty string, then the content attribute must be
removed, otherwise, the setter must raise a SYNTAX_ERR
exception.
If a reflecting DOM attribute is a DOMString 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 DOM attribute is a boolean attribute, then on
getting the DOM attribute must return true if the attribute is set,
and false if it is absent. On setting, the content attribute must be
removed if the DOM attribute is set to false, and must be set to
have the same value as its name if the DOM attribute is set to
true. (This corresponds to the rules for boolean content attributes.)
If a reflecting DOM attribute is 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 DOM 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 in base ten and then that string must
be used as the new content attribute value.
If a reflecting DOM attribute is 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 of the DOM 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 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
non-negative integer in base ten and then that string must be
used as the new content attribute value.
If a reflecting DOM attribute is an unsigned integer type
(unsigned long) that is limited to only positive
non-zero numbers, 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 of the DOM 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 zero, the user agent must fire an
INDEX_SIZE_ERR exception. Otherwise, the given value
must be converted to the shortest possible string representing the
number as a valid non-negative integer in base ten and
then that string must be used as the new content attribute
value.
If a reflecting DOM attribute is a floating point number type
(float) and it doesn't fall into one of the earlier
categories, then, 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 in the
range of the DOM 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 0.0 if there is no default value. On setting,
the given value must be converted to the best representation
of the floating point number and then that string must be
used as the new content attribute value.
The values ±Infinity and NaN throw an
exception on setting, as defined by Web IDL. [WEBIDL]
If a reflecting DOM attribute is of the type
DOMTokenList or DOMSettableTokenList, then
on getting it must return a DOMTokenList or
DOMSettableTokenList object (as appropriate) whose
underlying string is the element's corresponding content
attribute. When the object mutates its underlying string, the
content attribute must itself be immediately mutated. When the
attribute is absent, then the string represented by the object is
the empty string; when the object mutates this empty string, the
user agent must first add the corresponding content attribute, and
then mutate that attribute instead. The same
DOMTokenList object must be returned every time for
each attribute.
If a reflecting DOM attribute has the type
HTMLElement, or an interface that descends from
HTMLElement, then, on getting, it must run the
following algorithm (stopping at the first point where a value is
returned):
If the corresponding content attribute is absent, then the
DOM attribute must return null.
Let candidate be the element that the document.getElementById() method would find if it
was passed as its argument the current value of the corresponding
content attribute.
If candidate is null, or if it is not
type-compatible with the DOM attribute, then the DOM attribute must
return null.
Otherwise, it must return candidate.
On setting, if the given element has an id attribute, then the content attribute must
be set to the value of that id
attribute. Otherwise, the DOM attribute must be set to the empty
string.
When a collection is created, a
filter and a root are associated with the collection.
For example, when the HTMLCollection
object for the document.images attribute is
created, it is associated with a filter that selects only
img elements, and rooted at the root of the
document.
The collection then represents a
live view of the subtree rooted at the collection's
root, containing only nodes that match the given filter. The view is
linear. In the absence of specific requirements
to the contrary, the nodes within the collection must be sorted in
tree order.
Returns a collection that is a filtered view of the current collection, containing only elements with the given tag name.
The object's indices of the supported indexed
properties are the numbers in the range zero to one less than
the number of nodes represented by the collection. If
there are no such elements, then there are no supported
indexed properties.
The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must
return null.
Returns the item with ID or namename from the collection.
If there are multiple matching items, then a RadioNodeList object containing all those elements is returned.
Returns null if no element with that ID or name could be found.
radioNodeList . value [ = value ]
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 indices of the supported indexed
properties are the numbers in the range zero to one less than
the number of nodes represented by the collection. If
there are no such elements, then there are no supported
indexed properties.
The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must
return null.
The names of the supported named properties consist
of the values of all the id and name attributes of all the elements
represented by the collection.
The namedItem(name) method must act according to the
following algorithm:
If, at the time the method is called, there is exactly one node
in the collection that has either an id attribute or a name attribute equal to name, then return that node and stop the
algorithm.
Otherwise, if there are no nodes in the collection that have
either an id attribute or a name attribute equal to name, then return null and stop the algorithm.
If element is null, or if it is an
element with no value
attribute, return the empty string.
Otherwise, return the value of element's
value attribute.
On setting, the value DOM attribute must run
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 value content
attribute is present and equal to the new value, if any. Otherwise,
let it be null.
If element is not null, then set its
checkedness to true.
2.8.2.3 HTMLOptionsCollection
The HTMLOptionsCollection interface represents a
list of option elements. It is always rooted on a
select element and has attributes and methods that
manipulate that element's descendants.
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 HIERARCHY_REQUEST_ERR
exception if element is an ancestor of the
element into which it is to be inserted. If element is not an option or
optgroup element, then the method does nothing.
The object's indices of the supported indexed
properties are the numbers in the range zero to one less than
the number of nodes represented by the collection. If
there are no such elements, then there are no supported
indexed properties.
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). 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 item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must
return null.
The names of the supported named properties consist
of the values of all the id and name attributes of all the elements
represented by the collection.
The namedItem(name) method must act according to the
following algorithm:
If, at the time the method is called, there is exactly one node
in the collection that has either an id attribute or a name attribute equal to name, then return that node and stop the
algorithm.
Otherwise, if there are no nodes in the collection that have
either an id attribute or a name attribute equal to name, then return null and stop the algorithm.
Otherwise, create a NodeList object representing a
live view of the HTMLOptionsCollection object, further
filtered so that the only nodes in the NodeList object
are those that have either an id
attribute or a name attribute
equal to name. The nodes in the
NodeList object must be sorted in tree
order.
Return that NodeList object.
The add(element, before)
method must act according to the following algorithm:
If element is not an option
or optgroup element, then return and abort these
steps.
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 NOT_FOUND_ERR exception.
If element and before are the same element, then return and abort
these steps.
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.
Act as if the DOM Core insertBefore() method was invoked
on the parent node, with element as the first argument and reference as the second argument.
The remove(index) method must act according to
the following algorithm:
If index is not a number greater than or
equal to 0 and less than the number of nodes represented by
the collection, let element be the first
element in the collection. Otherwise, let element be the indexth element
in the collection.
Returns a PropertyNodeList object containing any elements that add a property named name.
propertyNodeList . content
Returns an array of the various values that the relevant elements have.
The object's indices of the supported indexed
properties are the numbers in the range zero to one less than
the number of nodes represented by the collection. If
there are no such elements, then there are no supported
indexed properties.
The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must
return null.
The names
attribute must return a live DOMStringList object
giving the property names of all the elements
represented by the collection, listed in tree
order, but with duplicates removed, leaving only the first
occurrence of each name. The same object must be returned each
time.
The namedItem(name) method must return a
PropertyNodeList object representing a live view of the
HTMLPropertyCollection object, further filtered so that
the only nodes in the RadioNodeList object are those
that have a property name equal
to name. The nodes in the
PropertyNodeList object must be sorted in tree
order, and the same object must be returned each time a
particular name is queried.
A members of the PropertyNodeList interface
inherited from the NodeList interface must behave as
they would on a NodeList object.
The content DOM
attribute on the PropertyNodeList object, on getting,
must return a newly constructed DOMStringArray whose
values are the values obtained from the content DOM property of each of the
elements represented by the object, in tree order.
While the order of the tokens in the underlying
string is not important, the DOMTokenList interfaces
preserves the underlying order for consistency between
implementations.
The object's indices of the supported indexed
properties are the numbers in the range zero to length-1, unless the length is zero, in which case
there are no supported indexed properties.
The item(index) method must split the underlying string on spaces,
preserving the order of the tokens as found in the underlying
string, remove instances of exact duplicates other than the first
instance in each case, and then return the indexth item in this list. If index is equal to or greater than the number of
tokens, then the method must return null.
For example, if the string is "a b
a c" then there are three tokens: the token with index 0 is
"a", the token with index 1 is "b", and the token with index 2 is "c".
The contains(token) method must run the following
algorithm:
If the given token is already one of the
tokens in the DOMTokenList object's underlying string
then stop the algorithm.
Otherwise, if the DOMTokenList object's underlying
string is not the empty string and the last character of that
string is not a space character, then append a U+0020
SPACE character to the end of that string.
Append the value of token to the end of the
DOMTokenList object's underlying string.
The remove(token) method must run the following
algorithm:
Otherwise, if the DOMTokenList object's underlying
string is not the empty string and the last character of that
string is not a space character, then append a U+0020
SPACE character to the end of that string.
Append the value of token to the end of the
DOMTokenList object's underlying string.
Return true.
Objects implementing the DOMTokenList interface must
stringify to the object's
underlying string representation.
2.8.4 DOMSettableTokenList
The DOMSettableTokenList interface is the same as the
DOMTokenList interface, except that it allows the
underlying string to be directly changed.
An object implementing the DOMSettableTokenList
interface must act as defined for the DOMTokenList
interface, except for the value attribute defined
here.
The value
attribute must return the underlying string on getting, and must
replace the underlying string with the new value on setting.
2.8.5 Safe passing of structured data
When a user agent is required to obtain a structured
clone of an object, it must run the following algorithm, which
either returns a separate object, or throws an exception.
Let input be the object being
cloned.
Let memory be a list of objects,
initially empty. (This is used to catch cycles.)
The internal structured cloning algorithm is always
called with two arguments, input and memory, and its behavior depends on the type of input, as follows:
If input is the undefined value
Return the undefined value.
If input is the null value
Return the null value.
If input is the false value
Return the false value.
If input is the true value
Return the true value.
If input is a Number object
Return a newly constructed Number object with the same value as input.
If input is a String object
Return a newly constructed String object with the same value as input.
If input is a Date object
Return a newly constructed Date object with the same value as input.
If input is a RegExp object
Return a newly constructed RegExp object with the same pattern and flags as input.
The value of the lastIndex property is not copied.
Return a newly constructed ImageData object
with the same width and
height as input, and with a newly constructed
CanvasPixelArray for its data attribute, with the same
length and pixel
values as the input's.
Otherwise, let new memory be a list
consisting of the items in memory with the
addition of input.
Create a new object, output, of the
same type as input: either an Array or an
Object.
For each enumerable property in input,
add a corresponding property to output
having the same name, and having a value created from invoking
the internal structured cloning algorithm
recursively with the value of the property as the "input" argument and new
memory as the "memory" argument. The
order of the properties in the input and
output objects must be the same.
This does not walk the prototype chain.
Return output.
If input is another native object type (e.g. Error)
Return the null value.
2.8.6 DOMStringMap
The DOMStringMap interface represents a set of
name-value pairs. It exposes these using the scripting language's
native mechanisms for property access.
When a DOMStringMap object is instantiated, it is
associated with three algorithms, one for getting the list of
name-value pairs, one for setting names to certain values, and one
for deleting names.
The names of the supported named properties on a
DOMStringMap object at any instant are the names of
each pair returned from the algorithm for getting the list of
name-value pairs at that instant.
When a DOMStringMap object is indexed to retrieve a
named property name, the value returned must be
the value component of the name-value pair whose name component is
name in the list returned by the algorithm for
getting the list of name-value pairs.
When a DOMStringMap object is indexed to create or
modify a named property name with value value, the algorithm for setting names to certain
values must be run, passing name as the name and
the result of converting value to a
DOMString as the value.
When a DOMStringMap object is indexed to delete a
named property named name, the algorithm for
deleting names must be run, passing name as the
name.
The DOMStringMap interface definition
here is only intended for JavaScript environments. Other language
bindings will need to define how DOMStringMap is to be
implemented for those languages.
The dataset attribute on
elements exposes the data-*
attributes on the element.
Given the following fragment and elements with similar
constructions:
...one could imagine a function splashDamage() that takes some arguments, the first
of which is the element to process:
function splashDamage(node, x, y, damage) {
if (node.classList.contains('tower') && // checking the 'class' attribute
node.dataset.x == x && // reading the 'data-x' attribute
node.dataset.y == y) { // reading the 'data-y' attribute
var hp = parseInt(node.dataset.hp); // reading the 'data-hp' attribute
hp = hp - damage;
if (hp < 0) {
hp = 0;
node.dataset.ai = 'dead'; // setting the 'data-ai' attribute
delete node.dataset.ability; // removing the 'data-ability' attribute
}
node.dataset.hp = hp; // setting the 'data-hp' attribute
}
}
2.8.7 DOM feature strings
DOM3 Core defines mechanisms for checking for interface support,
and for obtaining implementations of interfaces, using feature
strings. [DOM3CORE]
A DOM application can use the hasFeature(feature,
version) method of the
DOMImplementation interface with parameter values
"HTML" and "5.0" (respectively)
to determine whether or not this module is supported by the
implementation. In addition to the feature string "HTML", the feature string "XHTML" (with version string "5.0") can
be used to check if the implementation supports XHTML. User agents should respond with a true value when the
hasFeature method is queried with these values.
Authors are cautioned, however, that UAs returning true might not be
perfectly compliant, and that UAs returning false might well have
support for features in this specification; in general, therefore,
use of this method is discouraged.
The values "HTML" and "XHTML" (both with version "5.0") should
also be supported in the context of the getFeature()
and isSupported() methods, as defined by DOM3 Core.
The interfaces defined in this specification are not
always supersets of the interfaces defined in DOM2 HTML; some
features that were formerly deprecated, poorly supported, rarely
used or considered unnecessary have been removed. Therefore it is
not guaranteed that an implementation that supports "HTML" "5.0" also supports "HTML" "2.0".
2.8.8 Exceptions
The following DOMException codes are defined in DOM
Core. [DOMCORE]
INDEX_SIZE_ERR
DOMSTRING_SIZE_ERR
HIERARCHY_REQUEST_ERR
WRONG_DOCUMENT_ERR
INVALID_CHARACTER_ERR
NO_DATA_ALLOWED_ERR
NO_MODIFICATION_ALLOWED_ERR
NOT_FOUND_ERR
NOT_SUPPORTED_ERR
INUSE_ATTRIBUTE_ERR
INVALID_STATE_ERR
SYNTAX_ERR
INVALID_MODIFICATION_ERR
NAMESPACE_ERR
INVALID_ACCESS_ERR
VALIDATION_ERR
TYPE_MISMATCH_ERR
SECURITY_ERR
NETWORK_ERR
ABORT_ERR
URL_MISMATCH_ERR
QUOTA_EXCEEDED_ERR
DATAGRID_MODEL_ERR
PARSE_ERR
SERIALISE_ERR
2.8.9 Garbage collection
There is an implied strong reference from any DOM
attribute that returns a pre-existing object to that object.
For example, the document.location attribute means
that there is a strong reference from a Document
object to its Location object. Similarly, there is
always a strong reference from a Document to any
descendant nodes, and from any node to its owner
Document.
3 Semantics, structure, and APIs of HTML documents
3.1 Introduction
This section is non-normative.
An introduction to marking up a document.
3.2 Documents
Every XML and HTML document in an HTML UA is represented by a
Document object. [DOM3CORE]
Document objects are assumed to be XML
documents unless they are flagged as being HTML
documents when they are created. Whether a document is an
HTML document or an XML document affects the behavior of
certain APIs, as well as a few CSS rendering rules. [CSS]
A Document object created by the createDocument() API on the
DOMImplementation object is initially an XML document, but can be made into an
HTML document by calling document.open() on it.
3.2.1 Documents in the DOM
All Document objects (in user agents implementing
this specification) must also implement
the HTMLDocument interface, available using
binding-specific methods. (This is the case whether or not the
document in question is an HTML
document or indeed whether it contains any HTML
elements at all.) Document objects must also implement the document-level interface
of any other namespaces found in the document that the UA
supports.
For example, if an HTML implementation also
supports SVG, then the Document object implements both
HTMLDocument and SVGDocument.
Because the HTMLDocument interface is
now obtained using binding-specific casting methods instead of
simply being the primary interface of the document object, it is no
longer defined as inheriting from Document.
Since the HTMLDocument interface holds methods and
attributes related to a number of disparate features, the members of
this interface are described in various different sections.
Returns the
address 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 either the current address of the active document
of the source browsing contextat the time the
navigation was started (that is, the page which navigated the browsing context
to the current document), or the empty string if there is no such
originating page, or if the UA has been configured not to report
referrers in this case, or if the navigation was initiated for a
hyperlink with a noreferrer keyword.
In the case of HTTP, the referrer DOM attribute will
match the Referer (sic) header
that was sent when fetching the current
page.
Typically user agents are configured to not report
referrers in the case where the referrer uses an encrypted protocol
and the current page does not (e.g. when navigating from an https: page to an http:
page).
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.
On setting, if the document is not associated with a
browsing context then the user agent must raise an
INVALID_STATE_ERR exception. Otherwise, if the
sandboxed origin browsing context flag was set on the
browsing context of the Document when the
Document was created, the user agent must raise a
SECURITY_ERR exception. Otherwise, if the
document's address does not use a server-based naming
authority, it must do nothing. Otherwise, the user agent must
obtain the storage mutex and then act as it would when
processing cookies if it had just attempted to fetchthe document's address over HTTP, and had received a
response with a Set-Cookie header whose value was the
specified value, as per RFC 2109 sections 4.3.1, 4.3.2, and 4.3.3 or
later specifications, but without overwriting the values of
HTTP-only cookies. [RFC2109][RFC2965]
This specification does not define what makes an
HTTP-only cookie, and at the time of publication the editor is not
aware of any reference for HTTP-only cookies. They are a feature
supported by some Web browsers wherein an "httponly" parameter added to the cookie string
causes the cookie to be hidden from script.
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.
Returns the date of the last modification to the document, as
reported by the server, in the form "MM/DD/YYYY hh:mm:ss".
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:
The month component of the date.
A U+002F SOLIDUS character ('/').
The day component of the date.
A U+002F SOLIDUS character ('/').
The year component of the date.
A U+0020 SPACE character.
The hours component of the time.
A U+003A COLON character (':').
The minutes component of the time.
A U+003A COLON character (':').
The seconds component of the time.
All the numeric components above, other than the year, must be
given as two digits in the range U+0030 DIGIT ZERO to U+0039 DIGIT
NINE representing the number in base ten, zero-padded if
necessary. The year must be given as four or more digits in the
range U+0030 DIGIT ZERO to U+0039 DIGIT NINE 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.
In a conforming document, returns the string "CSS1Compat". (In quirks mode
documents, returns the string "BackCompat",
but a conforming document can never trigger quirks
mode.)
A Document is always set to one of three modes:
no quirks mode, the default; quirks mode, used
typically for legacy documents; and limited quirks mode,
also known as "almost standards" mode. The mode is only ever changed
from the default by the HTML parser, based on the
presence, absence, or value of the DOCTYPE string.
The compatMode DOM
attribute must return the literal string "CSS1Compat" unless the document has been set to
quirks mode by the HTML parser, in which
case it must instead return the literal string "BackCompat".
Returns what might be the user agent's default character encoding.
Documents have an associated character encoding. When a Document
object is created, the document's character encoding
must be initialized to UTF-16. Various algorithms during page
loading affect this value, as does the charset setter. [IANACHARSET]
The charset
DOM attribute must, on getting, return the preferred MIME name of
the document's character encoding. On setting, if the
new value is an IANA-registered alias for a character encoding
supported by the user agent, the document's character
encoding must be set to that character encoding. (Otherwise,
nothing happens.)
The characterSet
DOM attribute must, on getting, return the preferred MIME name of
the document's character encoding.
The defaultCharset
DOM attribute must, on getting, return the preferred MIME name of a
character encoding, possibly the user's default encoding, or an
encoding associated with the user's current geographical location,
or any arbitrary encoding name.
Returns "loading" while the Document is loading, and "complete" once it has loaded.
The readystatechange event fires on the Document object when this value changes.
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 or an
XML parser, or to the string "complete"
otherwise. Various algorithms during page loading affect this
value. When the value is set, the user agent must fire a
simple event called 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.
Can be set, to update the document's title. If there is no
head element,
the new value is ignored.
In SVG documents, the SVGDocument interface's
title attribute takes
precedence.
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 root element is an svg
element in the "http://www.w3.org/2000/svg"
namespace, and the user agent supports SVG, then return the value
that would have been returned by the DOM attribute of the same name
on the SVGDocument interface. [SVG]
On setting, the following algorithm must be run. Mutation events
must be fired as appropriate.
If the root element is an svg
element in the "http://www.w3.org/2000/svg"
namespace, and the user agent supports SVG, then the setter must
defer to the setter for the DOM attribute of the same name on the
SVGDocument interface (if it is readonly, then this
will raise an exception). Stop the algorithm here. [SVG]
A single Text node whose data is the new value
being assigned must be appended to the title
element.
The title attribute on
the HTMLDocument interface should shadow the attribute
of the same name on the SVGDocument interface when the
user agent supports both HTML and SVG. [SVG]
The body element of a document is the first child of
the html element that is either a
body element or a frameset element. If
there is no such element, it is null. If the body
element is null, then when the specification requires that events be
fired at "the body element", they must instead be fired at the
Document object.
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:
Otherwise, if the new value is the same as the body
element, do nothing. Abort these steps.
Otherwise, if the body element is not null, then
replace that element with the new value in the DOM, as if the root
element's replaceChild() method had been
called with the new value and the
incumbent body element as its two arguments respectively,
then abort these steps.
Otherwise, the the body element is null. Append
the new value to the root element.
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.
Returns a NodeList of the elements in the object
on which the method was invoked (a Document or an
Element) that have all the classes given by classes.
The classes argument is interpreted as a
space-separated list of classes.
The getElementsByClassName(classNames) method takes a string that
contains an unordered set of unique space-separated
tokens representing classes. When called, the method must
return a live NodeList object containing all the
elements in the document, in tree order, that have all
the classes specified in that argument, having obtained the classes
by splitting a string on
spaces. If there are no tokens specified in the argument,
then the method must return an empty NodeList. If the
document is in quirks mode, then the comparisons for
the classes must be done in an ASCII case-insensitive
manner, otherwise, the comparisons must be done in a
case-sensitive manner.
The getElementsByClassName(classNames) method on the
HTMLElement interface must return a live
NodeList with the nodes that the
HTMLDocumentgetElementsByClassName()
method would return when passed the same argument(s), excluding any
elements that are not descendants of the HTMLElement
object on which the method was invoked.
HTML, SVG, and MathML elements define which classes they are in
by having an attribute in the per-element partition with the name
class containing a space-separated list of
classes to which the element belongs. Other specifications may also
allow elements in their namespaces to be labeled as being in
specific classes.
A call to
document.getElementById('example').getElementsByClassName('aaa')
would return a NodeList with the two paragraphs
p1 and p2 in it.
A call to getElementsByClassName('ccc bbb')
would only return one node, however, namely p3. A call
to
document.getElementById('example').getElementsByClassName('bbb ccc ')
would return the same thing.
A call to getElementsByClassName('aaa,bbb') would
return no nodes; none of the elements above are in the "aaa,bbb"
class.
The HTMLDocument interface supports named properties. The names
of the supported named properties at any moment consist of
the values of the name content
attributes of all the applet, embed,
form, iframe, img, and
fallback-freeobject elements in the
Document that have name
content attributes, and the values of the id content attributes of all the
applet and fallback-freeobject elements in the Document that have
id content attributes, and the values
of the id content attributes of all the
img elements in the Document that have
both name content attributes and
id content attributes.
When the
HTMLDocument object is indexed for property
retrieval using a name name, then the user
agent must return the value obtained using the following steps:
Let elements be the list of named elements with
the name name in the Document.
There will be at least one such element, by
definition.
If elements has only one element, and that
element is an iframe element, then return the
WindowProxy object of the nested browsing
context represented by that iframe element,
and abort these steps.
Otherwise, if elements has only one
element, return that element and abort these steps.
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:
img elements that have an id content attribute whose value is name, and that have a name content attribute present also.
An object element is said to be
fallback-free if it has no object or
embed descendants.
The dir
attribute on the HTMLDocument interface is defined
along with the dir content
attribute.
3.3 Elements
3.3.1 Semantics
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.
Authors must not use elements, attributes, and attribute values
for purposes other than their appropriate intended semantic
purpose. Authors must not use elements, attributes, and attribute
values that are not permitted by this specification or other
applicable specifications.
For example, the following document is non-conforming, despite
being syntactically correct:
<!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="http://example.org/~ernest/"><cite>Ernest</cite></a>,
in an essay from 1992
</td>
</tr>
</table>
</body>
</html>
...because the data placed in the cells is clearly not tabular
data (and the cite element mis-used). 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="http://example.org/~ernest/">Ernest</a>,
in an essay from 1992
</p>
</body>
</html>
This next document fragment, intended to represent the heading
of a corporate site, is similarly 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>ABC Company</h1>
<h2>Leading the way in widget design since 1432</h2>
...
The hgroup element should be used in these kinds of
situations:
<body>
<hgroup>
<h1>ABC Company</h1>
<h2>Leading the way in widget design since 1432</h2>
</hgroup>
...
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:
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.
3.3.2 Elements in the DOM
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.
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.
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.
3.3.3 Global attributes
The following attributes are common to and may be specified on
all HTML elements (even those not
defined in this specification):
The attributes marked with an asterisk cannot be
specified on body elements as those elements expose
event handler attributes of the Window object with the same
names.
Also, custom data
attributes (e.g. data-foldername or
data-msgid) can be specified on any HTML element, to store custom data
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 XHTML 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.
3.3.3.1 The id attribute
The id attribute
represents its element's unique identifier. The value
must be unique in the element's home subtree and must
contain at least one character. The value must not contain any space characters.
If the value is not the empty string, user agents must associate
the element with the given value (exactly, including any space
characters) for the purposes of ID matching within the element's
home subtree (e.g. for selectors in CSS or for the
getElementById() method in the DOM).
Identifiers are opaque strings. Particular meanings should not be
derived from the value of the id
attribute.
This specification doesn't preclude an element having multiple
IDs, if other mechanisms (e.g. DOM Core methods) can set an
element's ID in a way that doesn't conflict with the id attribute.
The id DOM attribute must
reflect the id content
attribute.
3.3.3.2 The title attribute
The 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; and so forth. The
value is text.
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 title DOM attribute
must reflect the title
content attribute.
The 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 RFC 3066 language code, or
the empty string. [RFC3066]
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. Setting the attribute to the empty string indicates
that the primary language is unknown.
The lang attribute in no namespace
may be used on any HTML
element.
Authors must not use the lang attribute in the XML
namespace in HTML documents. To ease
migration to and from XHTML, 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.
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.
If there is no document-wide default language, then
language information from a higher-level protocol (such as HTTP), if
any, must be used as the final fallback language. In the absence of
any language information, the default value is unknown (the empty
string).
If the resulting value is not a recognized language code, then it
must be treated as an unknown language (as if the value was the
empty string).
User agents may use the element's language to determine proper
processing or rendering (e.g. in the selection of appropriate
fonts or pronunciations, or for dictionary selection).
The lang DOM attribute
must reflect the lang
content attribute in no namespace.
The dir attribute specifies the
element's text directionality. The attribute is an enumerated
attribute with the keyword ltr mapping
to the state ltr, and the keyword rtl
mapping to the state rtl. The attribute has no
defaults.
The processing of this attribute is primarily performed by the
presentation layer. For example, the rendering section in this
specification defines a mapping from this attribute to the CSS
'direction' and 'unicode-bidi' properties, and CSS defines rendering
in terms of those properties.
The directionality of an element, which is used in
particular by the canvas element's text rendering API,
is either 'ltr' or 'rtl'. If the user agent supports CSS and the
'direction' property on this element has a computed value of either
'ltr' or 'rtl', then that is the directionality of the
element. Otherwise, if the element is being rendered, then the
directionality of the element is the directionality used by
the presentation layer, potentially determined from the value of the
dir attribute on the
element. Otherwise, if the element's dir attribute has the state ltr, the
element's directionality is 'ltr' (left-to-right); if the attribute
has the state rtl, the element's directionality is 'rtl'
(right-to-left); and otherwise, the element's directionality is the
same as its parent element, or 'ltr' if there is no parent
element.
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).
The classes that an HTML
element has assigned to it consists of all the classes
returned when the value of the class
attribute is split on
spaces.
Assigning classes to an element affects class
matching in selectors in CSS, the getElementsByClassName()
method in the DOM, and other such features.
Authors may use any value in the class attribute, but are encouraged to use
the values that describe the nature of the content, rather than
values that describe the desired presentation of the
content.
The className and
classList DOM
attributes must both reflect the class content attribute.
3.3.3.7 The style attribute
All elements may have the style
content attribute set. If specified, the attribute must contain only
a list of zero or more semicolon-separated (;) CSS declarations. [CSS]
In user agents that support CSS, the attribute's value must be
parsed when the attribute is added or has its value changed, with
its value treated as the body (the part inside the curly brackets)
of a declaration block in a rule whose selector matches just the
element on which the attribute is set. All URLs in the value must be resolved relative to the element when the attribute is
parsed. For the purposes of the CSS cascade, the attribute must be
considered to be a 'style' attribute at the author level.
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 hidden attribute.)
Returns a CSSStyleDeclaration object for the element's style attribute.
The style DOM attribute
must return a CSSStyleDeclaration whose value
represents the declarations specified in the attribute, if
present. Mutating the CSSStyleDeclaration object must
create a style attribute on the
element (if there isn't one already) and then change its value to be
a value representing the serialized form of the
CSSStyleDeclaration object. [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>
3.3.3.8 Embedding custom non-visible data
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 characters in the range U+0041 .. U+005A (LATIN CAPITAL
LETTER A .. LATIN CAPITAL LETTER Z).
All attributes in HTML documents get
lowercased automatically, so the restriction on uppercase letters
doesn't affect such documents.
Custom data attributes
are intended to store custom data 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
independent of the site that uses the attributes.
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.
The dataset DOM
attribute provides convenient accessors for all the data-* attributes on an element. On
getting, the dataset DOM attribute
must return a DOMStringMap object, associated with the
following algorithms, which expose these attributes on their
element:
The algorithm for getting the list of name-value pairs
Let list be an empty list of name-value
pairs.
For each content attribute on the element whose first five
characters are the string "data-", add a
name-value pair to list whose name is the
attribute's name with the first five character removed and whose
value is the attribute's value.
Return list.
The algorithm for setting names to certain values
Let name be the concatenation of the
string data- and the name passed to the
algorithm.
Let value be the value passed to the
algorithm.
Set the value of the attribute with the name name, to the value value,
replacing any previous value if the attribute already existed. If
setAttribute() would have raised an
exception when setting an attribute with the name name, then this must raise the same
exception.
The algorithm for deleting names
Let name be the concatenation of the
string data- and the name passed to the
algorithm.
Remove the attribute with the name name,
if such an attribute exists. Do nothing otherwise.
If a Web page wanted an element to represent a space ship,
e.g. as part of a game, it would have to use the class attribute along with data-* attributes:
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.
3.4 Content models
All the elements in this specification have a defined content
model, which describes what nodes are allowed inside the elements,
and thus what the structure of an HTML document or fragment must
look like.
The space characters are
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 matches its content model or not, and must be
ignored when following algorithms that define document and element
semantics.
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.
Authors must not use elements in the HTML namespace
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 specification defines the Atom content element, when its type attribute has the value xhtml, as requiring that it contains 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]
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'),
};
3.4.1 Kinds of content
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:
In addition, certain elements are categorized as form-associated elements and
further subcategorized to define their role in various form-related
processing models.
Some elements have unique requirements and do not fit into any
particular category.
3.4.1.1 Metadata content
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#">
<head>
<title>Hedral's Home Page</title>
<r:RDF>
<Person xmlns="http://www.w3.org/2000/10/swap/pim/contact#"
r:about="http://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.
3.4.1.2 Flow content
Most elements that are used in the body of documents and
applications are categorized as flow content.
As a general rule, elements whose content model allows any
flow content should have either at least one descendant
text node that is not inter-element
whitespace, or at least one descendant element node that is
embedded content. For the purposes of this requirement,
del elements and their descendants must not be counted
as contributing to the ancestors of the del
element.
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.
3.4.1.3 Sectioning content
Sectioning content is content that defines the scope
of headings and footers.
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.
As a general rule, elements whose content model allows any
phrasing content should have either at least one
descendant text node that is not inter-element
whitespace, or at least one descendant element node that is
embedded content. For the purposes of this requirement,
nodes that are descendants of del elements must not be
counted as contributing to the ancestors of the del
element.
Most elements that are categorized as phrasing
content can only contain elements that are themselves categorized as
phrasing content, not any flow content.
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.
3.4.1.7 Interactive content
Interactive content is content that is specifically
intended for user interaction.
Certain elements in HTML have an activation
behavior, which means that the user can activate them. This
triggers a sequence of events dependent on the activation mechanism,
and normally culminating in a click
event followed by a DOMActivate event, as described below.
The user agent should allow the user to manually trigger elements
that have an activation behavior, for instance using
keyboard or voice input, or through mouse clicks. When the user
triggers an element with a defined activation behavior
in a manner other than clicking it, the default action of the
interaction event must be to run synthetic click activation
steps on the element.
The above doesn't happen for arbitrary synthetic
events dispatched by author script. However, the click() method can be used to make it
happen programmatically.
When a user agent is to run pre-click activation steps
on an element, it must run the pre-click activation steps
defined for that element, if any.
When a user agent is to run post-click activation
steps on an element, the user agent must fire a simple
event called DOMActivate that is cancelable at
that element. The default action of this event must be to run
final activation steps on that element. If the event is
canceled, the user agent must run canceled activation
steps on the element instead.
When a user agent is to run canceled activation steps
on an element, it must run the canceled activation steps
defined for that element, if any.
When a user agent is to run final activation steps on
an element, it must run the activation behavior defined
for that element. Activation behaviors can refer to the click and DOMActivate events that were fired
by the steps above leading up to this point.
3.4.2 Transparent content models
Some elements are described as transparent; they have
"transparent" in the description of their content model.
When a content model includes a part that is "transparent", those
parts must not contain content that would not be conformant if all
transparent elements in the tree were replaced, in their parent
element, by the children in the "transparent" part of their content
model, retaining order.
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.
3.5 Paragraphs
The term paragraph as defined in this
section is distinct from (though related to) the p
element defined later. The paragraph concept defined
here is used to describe how to interpret documents.
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, 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).
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.
<aside>
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.
</aside>
Here is another way of marking this up, this time showing the
paragraphs explicitly, and splitting the one link element into
three:
<aside>
<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>
</aside>
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="http://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:
The paragraph that says "You can play with my cat
simulator. object I'm quite proud of it.", where
object is the object element.
The paragraph that says "To see the cat simulator, use one of
the following links:".
The paragraph that says "Download simulator file".
The paragraph that says "Use online simulator".
The paragraph that says "Alternatively, upgrade to the Mellblom Browser.".
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.
3.6 APIs in HTML documents
For HTML documents, and for HTML
elements in HTML documents, certain APIs defined
in DOM3 Core become case-insensitive or case-changing, as sometimes
defined in DOM3 Core, and as summarized or
required below. [DOM3CORE].
These attributes must return element
names converted to ASCII uppercase, regardless of the case
with which they were created.
Document.createElement()
The canonical form of HTML markup is all-lowercase; thus, this
method will lowercase
the argument before creating the requisite element. Also, the element created must be in the HTML
namespace.
This doesn't apply to Document.createElementNS(). Thus, it is possible,
by passing this last method a tag name in the wrong case, to
create an element that claims to have the tag name of an element
defined in this specification, but doesn't support its interfaces,
because it really has another tag name not accessible from the DOM
APIs.
Specifically: when an attribute is set on an HTML element using Element.setAttribute(), the name argument must be
converted to ASCII lowercase before the element is
affected; and when an Attr node is set on an HTML element using Element.setAttributeNode(), it must have its name
converted to ASCII lowercase before the element is
affected.
This doesn't apply to Document.setAttributeNS() and Document.setAttributeNodeNS().
Specifically: When the Element.getAttribute() method or the Element.getAttributeNode() method is invoked on
an HTML element, the name
argument must be converted to ASCII lowercase before the
element's attributes are examined.
This doesn't apply to Document.getAttributeNS() and Document.getAttributeNodeNS().
Document.getElementsByTagName()
Element.getElementsByTagName()
HTML elements match by lower-casing the argument before
comparison, elements from other namespaces are treated as in XML
(case-sensitively).
Thus, in an HTML
document with nodes in multiple namespaces, these methods
will effectively be both case-sensitive and case-insensitive at
the same time.
3.7 Interactions with XPath and XSLT
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) are affected as
follows:
In addition to the cases where a name expression would match a
node per XPath 1.0, a name expression must evaluate to matching a
node when all the following conditions are also met:
The name expression has no namespace.
The name expression has local name that is a match for local.
The expression is being tested against an element node.
These requirements are 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]
3.8 Dynamic markup insertion
APIs for dynamically inserting markup into the
document interact with the parser, and thus their behavior, varies
depending on whether they are used with HTML documents
(and the HTML parser) or XHTML in XML
documents (and the XML parser).
3.8.1 Controlling the input stream
The open()
method comes in several variants with different numbers of
arguments.
Causes the Document to be replaced in-place, as if
it was a new Document object, but reusing the
previous object, which is then returned.
If the type argument is omitted or has the
value "text/html", then the resulting
Document has an HTML parser associated with it, which
can be given data to parse using document.write(). Otherwise, all
content passed to document.write() will be parsed
as plain text.
If the replace argument is absent or false,
a new entry is added to the session history to represent this
entry, and the previous entries for this Document are
all collapsed into one entry with a new Document
object.
The method has no effect if the Document is still
being parsed.
Closes the input stream that was opened by the document.open() method.
When called with two or fewer arguments, the method must act as
follows:
Let type be the value of the first
argument, if there is one, or "text/html"
otherwise.
Let replace be true if there is a second
argument and it is an ASCII case-insensitive match for
the value "replace", and false otherwise.
If the document has an active parser that isn't a
script-created parser, and the insertion
point associated with that parser's input
stream is not undefined (that is, it does point to
somewhere in the input stream), then the method does
nothing. Abort these steps and return the Document
object on which the method was invoked.
This basically causes document.open() to be ignored
when it's called in an inline script found during the parsing of
data sent over the network, while still letting it have an effect
when called asynchronously or on a document that is itself being
spoon-fed using these APIs.
If the document has an active parser, then
abort that parser, and throw away any pending content in the
input stream.
Unregister all event listeners registered on the
Document node and its descendants.
Remove any tasks
associated with the Document in any task
source.
Remove all child nodes of the document, without firing any
mutation events.
Replace the Document's singleton objects with
new instances of those objects. (This includes in particular the
Window, Location, History,
ApplicationCache, UndoManager,
Navigator, and Selection objects, the
various BarProp objects, the two Storage
objects, and the various HTMLCollection objects. It
also includes all the Web IDL prototypes in the JavaScript binding,
including the Document object's prototype.)
Create a new HTML parser and associate it with
the document. This is a script-created parser (meaning
that it can be closed by the document.open() and document.close() methods, and
that the tokenizer will wait for an explicit call to document.close() before emitting
an end-of-file token). The encoding confidence is
irrelevant.
Mark the document as being an HTML
document (it might already be so-marked).
If the type string contains a U+003B
SEMICOLON (;) character, remove the first such character and all
characters from it up to the end of the string.
Remove any earlier entries that share the same
Document
Add a new entry just before the last entry that is associated
with the text that was parsed by the previous parser associated
with the Document object, as well as the state of
the document at the start of these steps. (This allows the user
to step backwards in the session history to see the page before
it was blown away by the document.open() call.)
Finally, set the insertion point to point at
just before the end of the input stream (which at this
point will be empty).
Return the Document on which the method was
invoked.
When called with three or more arguments, the open() method on the
HTMLDocument object must call the open() method on the Window
object of the HTMLDocument object, with the same
arguments as the original call to the open() method, and return whatever
that method returned. If the HTMLDocument object has no
Window object, then the method must raise an
INVALID_ACCESS_ERR exception.
The close()
method must do nothing if there is no script-created
parser associated with the document. If there is such a
parser, then, when the method is called, the user agent must insert
an explicit "EOF" character at the end of the parser's
input stream.
