Web Applications 1.0

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 behaviour. The former category of requirements are requirements on documents and authoring tools. 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 XHTML5), and one using a custom format inspired by SGML (referred to as HTML5). Implementations may support only one of these two formats, although supporting both is encouraged.

XHTML documents (XML documents using elements from the HTML namespace) that use the new features described in this specification 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]

Such XML documents may contain a DOCTYPE if desired, but this is not required to conform to this specification.

HTML documents, if they are served over the wire (e.g. by HTTP) must be labelled 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.

A lot of arrays/lists/collections in this spec assume zero-based indexes but use the term "indexth" liberally. We should define those to be zero-based and be clearer about this.

1.3.1. Dependencies

This specification relies on several other underlying specifications.

XML

Implementations that support XHTML5 must support some version of XML, as well as its corresponding namespaces specification, because XHTML5 uses an XML serialisation with namespaces. [XML] [XMLNAMES]

XML Base

User agents must follow the rules given by XML Base to resolve relative URIs in HTML and XHTML fragments, because that is the mechanism used in this specification for resolving relative URIs in DOM trees. [XMLBASE]

It is possible for xml:base attributes to be present even in HTML fragments, as such attributes can be added dynamically using script.

DOM

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]

Implementations must support some version of the Window Object, because this specification extends this interface to provide some of its features. [WINDOW]

ECMAScript

Implementations that use ECMAScript to implement the APIs defined in this specification must implement them in a manner consistent with the ECMAScript Bindings for DOM Specifications specification, as this specification uses that specification's terminology. [EBFD]

This specification does not require support of any particular network transport protocols, image formats, audio formats, video formats, 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, ECMAScript as the scripting language, and HTTP as the network protocol, and several features assume that those languages and protocols are in use.

1.3.2. Features defined in other specifications

Some elements are defined in terms of their DOM textContent attribute. This is an attribute defined on the Node interface in DOM3 Core. [DOM3CORE]

Should textContent be defined differently for dir="" and AMPERSANDlt;bdo>? Should we come up with an alternative to textContent that handles those and other things, like alt=""?

The terms browsing context and top-level browsing context are used as defined in the Window Object specification. [WINDOW]

1.3.3. Relationship to HTML 4.01, XHTML 1.1, DOM2 HTML

This section is non-normative.

This specification represents a new version of HTML4 and XHTML1, along with a new version of the associated DOM2 HTML API. Migration from HTML4 or XHTML1 to the format and APIs described in this specification should in most cases be straightforward, as care has been taken to ensure that backwards-compatibility is retained.

This specification will eventually supplant Web Forms 2.0 as well. [WF2]

1.3.4. Relationship to XHTML2

This section is non-normative.

XHTML2 [XHTML2] defines a new HTML vocabulary with better features for hyperlinks, multimedia content, annotating document edits, rich metadata, declarative interactive forms, and describing the semantics of human literary works such as poems and scientific papers.

However, it lacks elements to express the semantics of many of the non-document types of content often seen on the Web. For instance, forum sites, auction sites, search engines, online shops, and the like, do not fit the document metaphor well, and are not covered by XHTML2.

This specification aims to extend HTML so that it is also suitable in these contexts.

XHTML2 and this specification use different namespaces and therefore can both be implemented in the same XML processor.

1.3.5. Relationship to XUL, WPF/XAML, and other proprietary UI languages

This section is non-normative.

This specification is independent of the various proprietary UI languages that various vendors provide.

1.4. 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 ECMAScript object properties and CSS properties. When these are ambiguous they are qualified as object properties and CSS properties respectively.

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).

The term HTML documents is sometimes used in contrast with XML documents to mean specifically documents that were parsed using an HTML parser (as opposed to using an XML parser or created purely through the DOM).

Generally, when the specification states that a feature applies to HTML or XHTML, 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 readability, the term URI is used to refer to both ASCII URIs and Unicode IRIs, as those terms are defined by [RFC3986] and [RFC3987] respectively. On the rare occasions where IRIs are not allowed but ASCII URIs are, this is called out explicitly.

The term root element, when not qualified to explicitly refer to the document's root element, means the furthest ancestor element node of whatever node is being discussed, or the node itself is there is none. 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.

An element is said to have been inserted into a document when its root element changes and is now the document's root element.

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.

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

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.

Various DOM interfaces are defined in this specification using pseudo-IDL. This looks like OMG IDL but isn't. For instance, method overloading is used, and types from the W3C DOM specifications are used without qualification. Language-specific bindings for these abstract interface definitions must be derived in the way consistent with W3C DOM specifications. Some interface-specific binding information for ECMAScript is included in this specification.

The current situation with IDL blocks is pitiful. IDL is totally inadequate to properly represent what objects have to look like in JS; IDL can't say if a member is enumerable, what the indexing behaviour is, what the stringification behaviour is, what behaviour setting a member whose type is a particular interface should be (e.g. setting of document.location or element.className), what constructor an object implementing an interface should claim to have, how overloads work, etc. I think we should make the IDL blocks non-normative, and/or replace them with something else that is better for JS while still being clear on how it applies to other languages. However, we do need to have something that says what types the methods take as arguments, since we have to raise exceptions if they are wrong.

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]

The term text node refers to any Text node, including CDATASection nodes (any Node with node type 3 or 4).

Some of the algorithms in this specification, for historical reasons, require the user agent to pause until some condition has been met. While a user agent is paused, it must ensure that no scripts execute (e.g. no event handlers, no timers, etc). User agents should remain responsive to user input while paused, however.

1.4.1. 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. Generally speaking, authors are discouraged from trying to use XML on the Web, because XML has much stricter syntax rules than the "HTML5" variant described above, and is relatively newer and therefore less mature.

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 "--AMPERSANDgt;" can be represented in "DOM5 HTML" but not in "HTML5" and "XHTML5". And so forth.

2. The Document Object Model

The Document Object Model (DOM) is a representation AMPERSANDmdash; a model AMPERSANDmdash; of a document and its content. [DOM3CORE] 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.

This specification defines the language represented in the DOM by features together called DOM5 HTML. DOM5 HTML consists of DOM Core Document nodes and DOM Core Element nodes, along with text nodes and other content.

Elements in the DOM represent things; that is, they have intrinsic meaning, also known as semantics.

For example, a p element represents a paragraph.

In addition, documents and elements in the DOM host APIs that extend the DOM Core APIs, providing new features to application developers using DOM5 HTML.

2.1. 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 behaviour of certain APIs, as well as a few CSS rendering rules. [CSS21]

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.

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 must implement 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.

interface HTMLDocument {  // Resource metadata management  readonly attribute DOMString URL;           attribute DOMString domain;  readonly attribute DOMString referrer;           attribute DOMString cookie;  // DOM tree accessors           attribute DOMString title;           attribute HTMLElement body;  readonly attribute HTMLCollection images;  readonly attribute HTMLCollection links;  readonly attribute HTMLCollection forms;  readonly attribute HTMLCollection anchors;  NodeList getElementsByName(in DOMString elementName);  NodeList getElementsByClassName(in DOMString[] classNames);  // Dynamic markup insertion           attribute DOMString innerHTML;  void open();  void open(in DOMString type);  void open(in DOMString type, in DOMString replace);  void open(in DOMString url, in DOMString name, in DOMString features);  void open(in DOMString url, in DOMString name, in DOMString features, in bool replace);  void close();  void write(in DOMString text);  void writeln(in DOMString text);  // Interaction  readonly attribute Element activeElement;  readonly attribute boolean hasFocus;  // Commands  readonly attribute HTMLCollection commands;  // Editing           attribute boolean designMode;  boolean execCommand(in DOMString commandID);  boolean execCommand(in DOMString commandID, in boolean doShowUI);  boolean execCommand(in DOMString commandID, in boolean doShowUI, in DOMString value);  Selection getSelection();  // Cross-document messaging  void postMessage(in DOMString message);  // lots of other stuff to come};

This specification requires that implementations also implement some version of the Window object specification, so all HTMLDocument objects also implement the DocumentWindow object and thus the DocumentView object.

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.

2.1.1. Resource metadata management

The URL attribute must return the the document's address.

The domain attribute must be initialised to the document's domain upon the creation of the Document object. On getting, the attribute must return its current value. On setting, if the new value is an allowed value (as defined below), the attribute's value must be changed to the new value. If the new value is not an allowed value, then a security exception must be raised instead.

A new value is an allowed value for the document.domain attribute if it is equal to the attribute's current value, or if the new value, prefixed by a U+002E FULL STOP ("."), exactly matches the end of the current value.

The domain attribute is used to enable pages on different hosts of a domain to access each others' DOMs.

The referrer attribute must return either the URI of the page which navigated the browsing context to the current document (if any), or the empty string (if there is no such originating page, or if the UA has been configured not to report referrers).

In the case of HTTP, the referrer DOM attribute will match the Referer (sic) header that was sent when fetching the current page.

The cookie attribute must, on getting, return the same string as the value of the Cookie HTTP header it would include if fetching the resource indicated by the document's address over HTTP, as per RFC 2109 section 4.3.4. [RFC2109]

On setting, the cookie attribute must cause the user agent to act as it would when processing cookies if it had just attempted to fetch the 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. [RFC2109]

2.2. Elements

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 XHTML elements in XML documents, even when those documents are in another context (e.g. inside an XSLT transform).

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.

interface HTMLElement : Element {  // DOM tree accessors  NodeList getElementsByClassName(in DOMString[] classNames);  // Dynamic markup insertion           attribute DOMString innerHTML;  // Metadata attributes           attribute DOMString id;           attribute DOMString title;           attribute DOMString lang;           attribute DOMString dir;           attribute DOMTokenString className;  // Interaction           attribute long tabindex;  void click();  void focus();  void blur();  // Commands           attribute HTMLMenuElement contextMenu;  // Editing           attribute boolean draggable;           attribute DOMString contenteditable;  // event handler DOM attributes           attribute EventListener onclick;           ...more events...};

As with the HTMLDocument 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.

2.2.1. 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.

If a reflecting DOM attribute is a DOMString attribute defined to contain a URI, then on getting, the DOM attribute must return the value of the content attribute, resolved to an absolute URI, 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 that is not defined to contain a URI, then the getting and setting must be done in a transparent, case-sensitive manner, except if the content attribute is defined to only allow a specific set of values. In this latter case, the attribute's value must first be converted to lowercase before being returned. 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 boolean attribute, then 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.

If a reflecting DOM attribute is a signed integer type (long) then the content attribute must be parsed according to the rules for parsing signed integers first. If that fails, 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 a 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 the content attribute must be parsed according to the rules for parsing unsigned integers first. If that fails, 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 a 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 of the type DOMTokenString, then on getting it must return the DOMTokenString object that represents the element's correspending content attribute, and on setting, the string representation of the new value must replace the value of the element's class content attribute, adding such an attribute if the element doesn't have one. The setter is unusual in that it expects a string, and does not affect the DOMTokenString object that is returned on getting. The same DOMTokenString object must be returned every time. When the attribute is absent, then the string represented by the DOMTokenString object is the empty string.

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):

1. If the corresponding content attribute is absent, then the DOM attribute must return null.
2. 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.
3. If candidate is null, or if it is not type-compatible with the DOM attribute, then the DOM attribute must return null.
4. 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.

2.3. Common DOM interfaces

2.3.1. Collections

The HTMLCollection, HTMLFormControlsCollection, and HTMLOptionsCollection interfaces represent various lists of DOM nodes. Collectively, objects implementing these interfaces are called collections.

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.

The rows list is not in tree order.

An attribute that returns a collection must return the same object every time it is retrieved.

2.3.1.1. HTMLCollection

The HTMLCollection interface represents a generic collection of elements.

interface HTMLCollection {  readonly attribute unsigned long length;  Element item(in unsigned long index);  Element namedItem(in DOMString name);};

The length attribute must return the number of nodes represented by the collection.

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 namedItem(key) method must return the first node in the collection that matches the following requirements:

• It is an a, applet, area, form, img, or object element with a name attribute equal to key, or,
• It is an HTML element of any kind with an id attribute equal to key. (Non-HTML elements, even if they have IDs, are not searched for the purposes of namedItem().)

If no such elements are found, then the method must return null.

In the ECMAScript DOM binding, objects implementing the HTMLCollection interface must support being dereferenced using the square bracket notation, such that dereferencing with an integer index is equivalent to invoking the item() method with that index, and such that dereferencing with a string index is equivalent to invoking the namedItem() method with that index.

2.3.1.2. HTMLFormControlsCollection

The HTMLFormControlsCollection interface represents a collection of form controls.

interface HTMLFormControlsCollection {  readonly attribute unsigned long length;  HTMLElement item(in unsigned long index);  Object namedItem(in DOMString name);};

The length attribute must return the number of nodes represented by the collection.

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 namedItem(key) method must act according to the following algorithm:

1. 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 key, then return that node and stop the algorithm.
2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to key, then return null and stop the algorithm.
3. Otherwise, create a NodeList object representing a live view of the HTMLFormControlsCollection 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 key. The nodes in the NodeList object must be sorted in tree order.
4. Return that NodeList object.

In the ECMAScript DOM binding, objects implementing the HTMLFormControlsCollection interface must support being dereferenced using the square bracket notation, such that dereferencing with an integer index is equivalent to invoking the item() method with that index, and such that dereferencing with a string index is equivalent to invoking the namedItem() method with that index.

2.3.1.3. HTMLOptionsCollection

The HTMLOptionsCollection interface represents a list of option elements.

interface HTMLOptionsCollection {           attribute unsigned long length;  HTMLOptionElement item(in unsigned long index);  Object namedItem(in DOMString name);};

On getting, the length attribute must return the number of nodes represented by the collection.

On setting, the behaviour 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 namedItem(key) method must act according to the following algorithm:

1. 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 key, then return that node and stop the algorithm.
2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to key, then return null and stop the algorithm.
3. 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 key. The nodes in the NodeList object must be sorted in tree order.
4. Return that NodeList object.

In the ECMAScript DOM binding, objects implementing the HTMLOptionsCollection interface must support being dereferenced using the square bracket notation, such that dereferencing with an integer index is equivalent to invoking the item() method with that index, and such that dereferencing with a string index is equivalent to invoking the namedItem() method with that index.

We may want to add add() and remove() methods here too because IE implements HTMLSelectElement and HTMLOptionsCollection on the same object, and so people use them almost interchangeably in the wild.

2.3.2. DOMTokenString

The DOMTokenString interface represents a string that consists of an unordered set of space-separated tokens.

interface DOMTokenString : DOMString {  boolean has(in DOMString token);  void add(in DOMString token);  void remove(in DOMString token);};

The has(token) method must run the following algorithm:

1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
3. If the token indicated by token is one of the tokens in the object's underlying string then return true and stop this algorithm.
4. Otherwise, return false.

The add(token) method must run the following algorithm:

1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
3. If the given token is already one of the tokens in the DOMTokenString object's underlying string then stop the algorithm.
4. Otherwise, if the last character of the DOMTokenString object's underlying string is not a space character, then append a U+0020 SPACE character to the end of that string.
5. Append the value of token to the end of the DOMTokenString object's underlying string.

The remove(token) method must run the following algorithm:

1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
2. Otherwise, remove the given token from the underlying string.

In the ECMAScript DOM binding, objects implementing the DOMTokenString interface must stringify to the object's underlying string representation.

DOMTokenString inherits from DOMString, so in bindings where strings have attributes or methods, those attributes and methods will also operate on DOMTokenString objects.

2.3.3. 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 guarenteed that an implementation that supports "HTML" "5.0" also supports "HTML" "2.0".

2.4. DOM tree accessors

The html element of a document is the document's root element, if there is one and it's an html element, or null otherwise.

The head element of a document is the first head element that is a child of the html element, if there is one, or null otherwise.

The title element of a document is the first title element that is a child of the head element, if there is one, or null otherwise.

The title attribute must, on getting, return a concatenation of the data of all the child text nodes of the title element, in tree order, or the empty string if the title element is null.

On setting, the following algorithm must be run:

1. If the head element is null, then the attribute must do nothing. Stop the algorithm here.
2. If the title element is null, then a new title element must be created and appended to the head element.
3. The children of the title element (if any) must all be removed.
4. A single Text node whose data is the new value being assigned must be appended to the title element.

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 followed:

1. If the new value is not a body or frameset element, then raise a HIERARCHY_REQUEST_ERR exception and abort these steps.
2. Otherwise, if the new value is the same as the body element, do nothing. Abort these steps.
3. 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.
4. 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 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 anchors attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with name attributes.

The getElementsByName(name) method a string name, and must return a live NodeList containing all the a, applet, button, form, iframe, img, input, map, meta, object, select, and textarea elements in that document that have a name attribute whose value is equal to the name argument.

The getElementsByClassName(classNames) method takes an array of strings representing classes. When called, the method must return a live NodeList object containing all the elements in the document that have all the classes specified in that array. If the array is empty, then the method must return an empty NodeList.

HTML, XHTML, 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 labelled as being in specific classes. UAs must not assume that all attributes of the name class for elements in any namespace work in this way, however, and must not assume that such attributes, when used as global attributes, label other elements as being in specific classes.

AMPERSANDlt;div id="example"AMPERSANDgt; AMPERSANDlt;p id="p1" class="aaa bbb"/AMPERSANDgt; AMPERSANDlt;p id="p2" class="aaa ccc"/AMPERSANDgt; AMPERSANDlt;p id="p3" class="bbb ccc"/AMPERSANDgt;AMPERSANDlt;/divAMPERSANDgt;

The getElementsByClassName() method on the HTMLElement interface must return the nodes that the HTMLDocument getElementsByClassName() method would return, excluding any elements that are not descendants of the HTMLElement object on which the method was invoked.

2.5. Dynamic markup insertion

The document.write() family of methods and the innerHTML family of DOM attributes enable script authors to dynamically insert markup into the document.

bz argues that innerHTML should be called something else on XML documents and XML elements. Is the sanity worth the migration pain?

Because these APIs interact with the parser, their behaviour varies depending on whether they are used with HTML documents (and the HTML parser) or XHTML in XML documents (and the XML parser). The following table cross-references the various versions of these APIs.

Regardless of the parsing mode, the document.writeln(s) method must call the document.write() method with the same argument s, and then call the document.write() method with, as its argument, a string consisting of a single newline character (U+000A).

2.5.1. Controlling the input stream

The open() method comes in several variants with different numbers of arguments.

When called with two or fewer arguments, the method must act as follows:

1. Let type be the value of the first argument, if there is one, or "text/html" otherwise.

2. Let replace be true if there is a second argument and it has the value "replace", and false otherwise.

3. 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.

   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.

4. Otherwise, if the document has an active parser, then stop that parser, and throw away any pending content in the input stream. what about if it doesn't, because it's either like a text/plain, or Atom, or PDF, or XHTML, or image document, or something?

5. Remove all child nodes of the document.

6. 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 tokeniser will wait for an explicit call to document.close() before emitting an end-of-file token).

7. Mark the document as being an HTML document (it might already be so-marked).

8. If type does not have the value "text/html", then act as if the tokeniser had emitted a pre element start tag, then set the HTML parser's tokenisation stage's content model flag to PLAINTEXT.

9. If replace is false, then: remove all the entries in the browsing context's session history after the current entry in its DocumentUI's History object, add a new entry whose address is the same as the current entry's at the end of the list, and then advance to that page as if the history.forward() method had been invoked.

10. Finally, set the insertion point to point at just before the end of the input stream (which at this point will be empty).

We shouldn't hard-code text/plain there. We should do it some other way, e.g. hand off to the section on content-sniffing and handling of incoming data streams, the part that defines how this all works when stuff comes over the network.

When called with three or more arguments, the open() method on the HTMLDocument object must call the open() method on the WindowHTML interface of the object returned by the defaultView attribute of the DocumentView interface of the HTMLDocument object, with the same arguments as the original call to the open() method. If the defaultView attribute of the DocumentView interface of the HTMLDocument object is null, 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 insertion point of the parser's input stream.

2.5.2. Dynamic markup insertion in HTML

In HTML, the document.write(s) method must act as follows:

1. If the insertion point is undefined, the open() method must be called (with no arguments) on the document object. The insertion point will point at just before the end of the (empty) input stream.

2. The string s must be inserted into the input stream just before the insertion point.

3. If there is a script that will execute as soon as the parser resumes, then the method must now return without further processing of the input stream.

4. Otherwise, the tokeniser must process the characters that were inserted, one at a time, processing resulting tokens as they are emitted, and stopping when the tokeniser reaches the insertion point or when the processing of the tokeniser is aborted by the tree construction stage (this can happen if a script start tag token is emitted by the tokeniser).

   If the document.write() method was called from script executing inline (i.e. executing because the parser parsed a set of script tags), then this is a reentrant invocation of the parser.

5. Finally, the method must return.

In HTML, the innerHTML DOM attribute of all HTMLElement and HTMLDocument nodes returns a serialisation of the node's children using the HTML syntax. On setting, it replaces the node's children with new nodes that result from parsing the given value. The formal definitions follow.

On getting, the innerHTML DOM attribute must return the result of running the following algorithm:

1. Let s be a string, and initialise it to the empty string.

2. For each child node child, in tree order, append the appropriate string from the following list to s:

   If the child node is an Element

   Append a U+003C LESS-THAN SIGN (AMPERSANDlt;) character, followed by the element's tag name (which is all lowercase).

   For each attribute that the element has, append a U+0020 SPACE character, the attribute's name (which again will be all lowercase), a U+003D EQUALS SIGN (=) character, a U+0022 QUOTATION MARK (AMPERSANDquot;) character, the attribute's value, escaped as described below, and a second U+0022 QUOTATION MARK (AMPERSANDquot;) character.

   While the exact order of attributes is UA-defined, and may depend on factors such as the order that the attributes were given in the original markup, the sort order must be stable, such that consecutive calls to innerHTML serialise an element's attributes in the same order.

   Append a U+003E GREATER-THAN SIGN (AMPERSANDgt;) character.

   If the child node is an Element with a tag name that is one of area, base, basefont, bgsound, br, col, embed, frame, hr, img, input, link, meta, param, spacer, or wbr, then continue on to the next child node at this point.

   Otherwise, append the value of the child element's innerHTML DOM attribute (thus recursing into this algorithm for that element), followed by a U+003C LESS-THAN SIGN (AMPERSANDlt;) character, a U+002F SOLIDUS (/) character, the element's tag name again (which is again all lowercase), and finally a U+003E GREATER-THAN SIGN (AMPERSANDgt;) character.

   If the child node is a Text or CDATASection node

   If one of the ancestors of the child node is a style, script, xmp, iframe, noembed, noframes, or noscript element, then append the value of the child node's data DOM attribute literally.

   Otherwise, append the value of the child node's data DOM attribute, escaped as described below.

   If the child node is a Comment

   Append the literal string AMPERSANDlt;!-- (U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS), followed by the value of the child node's data DOM attribute, followed by the literal string --AMPERSANDgt; (U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E GREATER-THAN SIGN).

   If the child node is a DocumentType

   Append the literal string AMPERSANDlt;!DOCTYPE (U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+0044 LATIN CAPITAL LETTER D, U+004F LATIN CAPITAL LETTER O, U+0043 LATIN CAPITAL LETTER C, U+0054 LATIN CAPITAL LETTER T, U+0059 LATIN CAPITAL LETTER Y, U+0050 LATIN CAPITAL LETTER P, U+0045 LATIN CAPITAL LETTER E), followed by a space (U+0020 SPACE), followed by the value of the child node's name DOM attribute, followed by the literal string AMPERSANDgt; (U+003E GREATER-THAN SIGN).

   Other nodes types (e.g. Attr) cannot occur as children of elements. If they do, the innerHTML attribute must raise an INVALID_STATE_ERR exception.

3. The result of the algorithm is the string s.

Escaping a string (for the purposes of the algorithm above) consists of replacing any occurances of the "AMPERSANDamp;" character by the string "AMPERSANDamp;amp;", any occurances of the "AMPERSANDlt;" character by the string "AMPERSANDamp;lt;", any occurances of the "AMPERSANDgt;" character by the string "AMPERSANDamp;gt;", and any occurances of the "AMPERSANDquot;" character by the string "AMPERSANDamp;quot;".

Entity reference nodes are assumed to be expanded by the user agent, and are therefore not covered in the algorithm above.

If the element's contents are not conformant, it is possible that the roundtripping through innerHTML will not work. For instance, if the element is a textarea element to which a Comment node has been appended, then assigning innerHTML to itself will result in the comment being displayed in the text field. Similarly, if, as a result of DOM manipulation, the element contains a comment that contains the literal string "--AMPERSANDgt;", then when the result of serialising the element is parsed, the comment will be truncated at that point and the rest of the comment will be interpreted as markup. Another example would be making a script element contain a text node with the text string "AMPERSANDlt;/script>".

On setting, if the node is a document, the innerHTML DOM attribute must run the following algorithm:

1. Otherwise, if the document has an active parser, then stop that parser, and throw away any pending content in the input stream. what about if it doesn't, because it's either like a text/plain, or Atom, or PDF, or XHTML, or image document, or something?

2. The user agent must remove the children nodes of the Document whose innerHTML attribute is being set.

3. The user agent must create a new HTML parser, in its initial state, and associate it with the Document node.

4. The user agent must place into the input stream for the HTML parser just created the string being assigned into the innerHTML attribute.

5. The user agent must start the parser and let it run until it has consumed all the characters just inserted into the input stream. (The Document node will have been populated with elements and a load event will have fired on its body element.)

Otherwise, if the node is an element, then setting the innerHTML DOM attribute must cause the following algorithm to run instead:

1. The user agent must create a new Document node, and mark it as being an HTML document.

   The user agent must create a new HTML parser, and associate it with the just created Document node.

   Parts marked innerHTML case in algorithms in the parser section are parts that only occur if the parser was created for the purposes of handling the setting of an element's innerHTML attribute. The algorithms have been annotated with such markings for informational purposes only; such markings have no normative weight. If it is possible for a condition described as an innerHTML case to occur even when the parser wasn't created for the purposes of handling an element's innerHTML attribute, then that is an error in the specification.

2. The user agent must set the HTML parser's tokenisation stage's content model flag according to the name of the element whose innerHTML attribute is being set, as follows:

   If it is a title or textarea element

   Set the content model flag to RCDATA.

   If it is a style, script, xmp, iframe, noembed, noframes, or noscript element

   Set the content model flag to CDATA.

   If it is a plaintext element

   Set the content model flag to PLAINTEXT.

   Otherwise

   Set the content model flag to PCDATA.

3. The user agent must switch the HTML parser's tree construction stage to the main phase.

4. Let root be a new html element with no attributes.

5. The user agent must append the element root to the Document node created above.

6. The user agent must set up the parser's stack of open elements so that it contains just the single element root.

7. The user agent must reset the parser's insertion mode appropriately.

8. The user agent must set the parser's form element pointer to the nearest node to the element whose innerHTML attribute is being set that is a form element (going straight up the ancestor chain, and including the element itself, if it is a form element), or, if there is no such form element, to null.

9. The user agent must place into the input stream for the HTML parser just created the string being assigned into the innerHTML attribute.

10. The user agent must start the parser and let it run until it has consumed all the characters just inserted into the input stream.

11. The user agent must remove the children of the element whose innerHTML attribute is being set.

12. The user agent must move all the child nodes of the root element to the element whose innerHTML attribute is being set, preserving their order.

2.5.3. Dynamic markup insertion in XML

In an XML context, the document.write(s) method must raise an INVALID_ACCESS_ERR exception.

The innerHTML attributes, on the other hand, in an XML context, are usable.

On getting, the innerHTML DOM attribute on HTMLElements and HTMLDocuments, in an XML context, must return a namespace-well-formed XML representation of the element or document. User agents may adjust prefixes and namespace declarations in the serialisation (and indeed might be forced to do so in some cases to obtain namespace-well-formed XML). [XML] [XMLNS]

On setting, if the node is a document, the innerHTML DOM attribute on must run the following algorithm:

1. The user agent must remove the children nodes of the Document whose innerHTML attribute is being set.

2. The user agent must create a new XML parser.

3. If the innerHTML attribute is being set on an element, the user agent must feed the parser just created the string corresponding to the start tag of that element, declaring all the namespace prefixes that are in scope on that element in the DOM, as well as declaring the default namespace (if any) that is in scope on that element in the DOM.

4. The user agent must feed the parser just created the string being assigned into the innerHTML attribute.

5. If the innerHTML attribute is being set on an element, the user agent must feed the parser the string corresponding to the end tag of that element.

6. If the parser found a well-formedness error, the attribute's setter must raise a SYNTAX_ERR exception and abort these steps.

7. Otherwise, the user agent must take the children of the document, if the attribute is being set on a Document node, or of the document's root element, if the attribute is being set on an Element node, and append them to the node whose innerHTML attribute is being set, preserving their order.

2.6. 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 summarised or required below. [DOM3CORE].

This does not apply to XML documents or to elements that are not in the HTML namespace despite being in HTML documents.

Element.tagName, Node.nodeName, and Node.localName

These attributes return tag names in all 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 HTML element, but doesn't support its interfaces, because it really has another tag name not accessible from the DOM APIs.

Element.setAttributeNode()

When an Attr node is set on an HTML element, it must have its name lowercased before the element is affected.

This doesn't apply to Document.setAttributeNodeNS().

Element.setAttribute()

When an attribute is set on an HTML element, the name argument must be lowercased before the element is affected.

This doesn't apply to Document.setAttributeNS().

Document.getElementsByTagName() and Element.getElementsByTagName()

These methods (but not their namespaced counterparts) must compare the given argument case-insensitively when looking at HTML elements, and case-sensitively otherwise.

Thus, in an HTML document with nodes in multiple namespaces, these methods will be both case-sensitive and case-insensitive at the same time.

Document.renameNode()

If the new namespace is the HTML namespace, then the new qualified name must be lowercased before the rename takes place.

3. Semantics and structure of HTML elements

3.1. Introduction

This section is non-normative.

An introduction to marking up a document.

3.2. 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.

Somewhere we need to define case-sensitivity of attribute values. e.g. contenteditable="TrUe" in HTML vs XHTML. Same with leading/trailing whitespace.

Need to go through the whole spec and make sure all the attribute values are clearly defined either in terms of microsyntaxes or in terms of other specs, or as "Text" or some such.

3.2.1. 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+000B LINE TABULATION, U+000C FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).

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:

1. Let input and position be the same variables as those of the same name in the algorithm that invoked these steps.

2. Let result be the empty string.

3. 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.

4. Return result.

The step skip whitespace means that the user agent must collect a sequence of characters that are space characters. The step skip Zs characters means that the user agent must collect a sequence of characters that are in the Unicode character class Zs. In both cases, the collected characters are not used. [UNICODE]

Similarly, when the algorithms below say to

3.2.2. Numbers

3.2.2.1. Unsigned integers

A string is a valid non-negative integer if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).

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 indeed any trailing garbage characters are ignored.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Let value have the value 0.

4. Skip whitespace.

5. If position is past the end of input, return an error.

6. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

7. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

   1. Multiply value by ten.
   2. Add the value of the current character (0..9) to value.
   3. Advance position to the next character.
   4. If position is not past the end of input, return to the top of step 7 in the overall algorithm (that's the step within which these substeps find themselves).

8. Return value.

3.2.2.2. Signed integers

A string is a valid integer if it consists of one of 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.

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.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Let value have the value 0.

4. Let sign have the value "positive".

5. Skip whitespace.

6. If position is past the end of input, return an error.

7. If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS ("-") character:

   1. Let sign be "negative".
   2. Advance position to the next character.
   3. If position is past the end of input, return an error.

8. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

9. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

   1. Multiply value by ten.
   2. Add the value of the current character (0..9) to value.
   3. Advance position to the next character.
   4. 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).

10. If sign is "positive", return value, otherwise return 0-value.

3.2.2.3. Real numbers

A string is a valid floating point number if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), optionally with a single U+002E FULL STOP (".") character somewhere (either before these numbers, in between two numbers, or after the numbers), all optionally prefixed with a U+002D HYPHEN-MINUS ("-") character.

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 a value. This algorithm will either return a number or an error. Leading spaces are ignored. Trailing spaces and garbage characters are ignored.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Let value have the value 0.

4. Let sign have the value "positive".

5. Skip whitespace.

6. If position is past the end of input, return an error.

7. If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS ("-") character:

   1. Let sign be "negative".
   2. Advance position to the next character.
   3. If position is past the end of input, return an error.

8. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9) or U+002E FULL STOP ("."), then return an error.

9. If the next character is U+002E FULL STOP ("."), but either that is the last character or the character after that one is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

10. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply value by ten.
    2. Add the value of the current character (0..9) to value.
    3. Advance position to the next character.
    4. If position is past the end of input, then if sign is "positive", return value, otherwise return 0-value.
    5. Otherwise return to the top of step 10 in the overall algorithm (that's the step within which these substeps find themselves).

11. Otherwise, if the next character is not a U+002E FULL STOP ("."), then if sign is "positive", return value, otherwise return 0-value.

12. The next character is a U+002E FULL STOP ("."). Advance position to the character after that.

13. Let divisor be 1.

14. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply divisor by ten.
    2. Add the value of the current character (0..9) divided by divisor, to value.
    3. Advance position to the next character.
    4. If position is past the end of input, then if sign is "positive", return value, otherwise return 0-value.
    5. Otherwise return to the top of step 14 in the overall algorithm (that's the step within which these substeps find themselves).

15. Otherwise, if sign is "positive", return value, otherwise return 0-value.

3.2.2.4. 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.

The steps for finding one or two numbers of a ratio in a string are as follows:

1. If the string is empty, then return nothing and abort these steps.
2. Find a number in the string according to the algorithm below, starting at the start of the string.
3. If the sub-algorithm in step 2 returned nothing or returned an error condition, return nothing and abort these steps.
4. Set number1 to the number returned by the sub-algorithm in step 2.
5. Starting with the character immediately after the last one examined by the sub-algorithm in step 2, skip any characters in the string that are in the Unicode character class Zs (this might match zero characters). [UNICODE]
6. 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.
7. 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.
8. Otherwise, if denominator was given a value in step 6, return number1 and denominator and abort these steps.
9. Find a number in the string again, starting immediately after the last character that was examined by the sub-algorithm in step 2.
10. If the sub-algorithm in step 9 returned nothing or an error condition, return nothing and abort these steps.
11. Set number2 to the number returned by the sub-algorithm in step 9.
12. 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.
13. 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.
14. 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.

1. 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.
2. If there are no such characters, return nothing and abort these steps.
3. 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.
4. If string contains more than one U+002E FULL STOP character then return an error condition and abort these steps.
5. Parse string according to the rules for parsing floating point number values, to obtain number. This step cannot fail (string is guarenteed to be a valid floating point number).
6. Return number.

3.2.2.5. Percentages and dimensions

valid non-negative percentages, rules for parsing dimension values

3.2.3. 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]

3.2.3.1. Specific moments in time

A string is a valid datetime if it has four digits (representing the year), a literal hyphen, two digits (representing the month), a literal hyphen, two digits (representing the day), optionally some spaces, either a literal T or a space, optionally some more spaces, two digits (for the hour), a colon, two digits (the minutes), another colon, two digits (the integer part of the seconds), optionally a decimal point followed by one or more digits (for the fractional part of the seconds), optionally some spaces, and finally either a literal Z (indicating the time zone is UTC), or, a plus sign or a minus sign followed by two digits, a colon, and two digits (for the sign, the hours and minutes of the timezone offset respectively); with the month-day combination being a valid date in the given year according to the Gregorian calendar, the hour values (h) being in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;hAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;23, the minute values (m) in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;mAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;59, and the second value (s) being in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;hAMPERSANDnbsp;AMPERSANDlt;AMPERSANDnbsp;60. [GREGORIAN]

The digits must be characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), the hyphens must be a U+002D HYPHEN-MINUS characters, the T must be a U+0054 LATIN CAPITAL LETTER T, the colons must be U+003A COLON characters, the decimal point must be a U+002E FULL STOP, the Z must be a U+005A LATIN CAPITAL LETTER Z, the plus sign must be a U+002B PLUS SIGN, and the minus U+002D (same as the hyphen).

Conformance checkers can use the algorithm below to determine if a datetime is a valid datetime or not.

To parse a string as a datetime value, a user agent must apply the following algorithm to the string. This will either return a time in UTC, with associated timezone information for round tripping or display purposes, or nothing, indicating the value is not a valid datetime. If at any point the algorithm says that it "fails", this means that it returns nothing.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. 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 four characters long, then fail. Otherwise, interpret the resulting sequence as a base ten integer. Let that number be the year.

4. 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.

5. 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.

6. If month is not a number in the range 1AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;monthAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;12, then fail.

7. Let maxday be the number of days in month month of year year.

8. 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.

9. 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.

10. If day is not a number in the range 1AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;monthAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;maxday, then fail.

11. Collect a sequence of characters that are either U+0054 LATIN CAPITAL LETTER T characters or space characters. If the collected sequence is zero characters long, or if it contains more than one U+0054 LATIN CAPITAL LETTER T character, then fail.

12. 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.

13. If hour is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;hourAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;23, then fail.

14. 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.

15. 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.

16. If minute is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;minuteAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;59, then fail.

17. Let second be a string with the value "0".

18. If position is beyond the end of input, then fail.

19. If the character at position is a U+003A COLON, then:

    1. Advance position to the next character in input.

    2. 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.

    3. 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.

20. Interpret second as a base ten number (possibly with a fractional part). Let that number be second instead of the string version.

21. If second is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;hourAMPERSANDnbsp;AMPERSANDlt;AMPERSANDnbsp;60, then fail. (The values 60 and 61 are not allowed: leap seconds cannot be represented by datetime values.)

22. If position is beyond the end of input, then fail.

23. Skip whitespace.

24. If the character at position is a U+005A LATIN CAPITAL LETTER Z, then:

    1. Let timezone_hours be 0.

    2. Let timezone_minutes be 0.

    3. Advance position to the next character in input.

25. Otherwise, if the character at position is either a U+002B PLUS SIGN ("+") or a U+002D HYPHEN-MINUS ("-"), then:

    1. 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".

    2. Advance position to the next character in input.

    3. 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 timezone_hours.

    4. If timezone_hours is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;timezone_hoursAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;23, then fail.
    5. If sign is "negative", then negate timezone_hours.

    6. 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.

    7. 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 timezone_minutes.

    8. If timezone_minutes is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;timezone_minutesAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;59, then fail.

26. If position is not beyond the end of input, then fail.

27. Let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, adding timezone_hours hours and timezone_minutes minutes. That moment in time is a moment in the UTC timezone.

28. Let timezone be timezone_hours hours and timezone_minutes minutes from UTC.

29. Return time and timezone.

3.2.3.2. Vaguer moments in time

This section defines date or time strings. There are two kinds, date or time strings in content, and date or time strings in attributes. The only difference is in the handling of whitespace characters.

To parse a date or time string, user agents must use the following algorithm. A date or time string is a valid date or time string if the following algorithm, when run on the string, doesn't say the string is invalid.

The algorithm may return nothing (in which case the string will be invalid), or it may return a date, a time, a date and a time, or a date and a time and and a timezone. Even if the algorithm returns one or more values, the string can still be invalid.

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Let results be the collection of results that are to be returned (one or more of a date, a time, and a timezone), initially empty. If the algorithm aborts at any point, then whatever is currently in results must be returned as the result of the algorithm.

4. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

6. Let the sequence of characters collected in the last step be s.

7. If position is past the end of input, the string is invalid; abort these steps.

8. If the character at position is not a U+003A COLON character, then:

   1. If the character at position is not a U+002D HYPHEN-MINUS ("-") character either, then the string is invalid, abort these steps.

   2. If the sequence s is not exactly four digits long, then the string is invalid. (This does not stop the algorithm, however.)

   3. Interpret the sequence of characters collected in step 5 as a base ten integer, and let that number be year.

   4. Advance position past the U+002D HYPHEN-MINUS ("-") character.

   5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

   6. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

   7. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be month.

   8. If month is not a number in the range 1AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;monthAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;12, then the string is invalid, abort these steps.

   9. Let maxday be the number of days in month month of year year.

   10. If position is past the end of input, or if the character at position is not a U+002D HYPHEN-MINUS ("-") character, then the string is invalid, abort these steps. Otherwise, advance position to the next character.

   11. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

   12. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

   13. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be day.

   14. If day is not a number in the range 1AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;dayAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;maxday, then the string is invalid, abort these steps.

   15. Add the date represented by year, month, and day to the results.

   16. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

   17. If the character at position is a U+0054 LATIN CAPITAL LETTER T, then move position forwards one character.

   18. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

   19. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

   20. Let s be the sequence of characters collected in the last step.

9. If s is not exactly two digits long, then the string is invalid.

10. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be hour.

11. If hour is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;hourAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;23, then the string is invalid, abort these steps.

12. If position is past the end of input, or if the character at position is not a U+003A COLON character, then the string is invalid, abort these steps. Otherwise, advance position to the next character.

13. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

14. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

15. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be minute.

16. If minute is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;minuteAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;59, then the string is invalid, abort these steps.

17. Let second be 0. It may be changed to another value in the next step.

18. If position is not past the end of input and the character at position is a U+003A COLON character, then:

    1. Collect a sequence of characters that are either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) or are U+002E FULL STOP. If the collected sequence is empty, or contains more than one U+002E FULL STOP character, then the string is invalid; abort these steps.

    2. If the first character in the sequence collected in the last step is not in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then the string is invalid.

    3. Interpret the sequence of characters collected two steps ago as a base ten number (possibly with a fractional part), and let that number be second.

    4. If second is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;minuteAMPERSANDnbsp;AMPERSANDlt;AMPERSANDnbsp;60, then the string is invalid, abort these steps.

19. Add the time represented by hour, minute, and second to the results.

20. If results has both a date and a time, then:

    1. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

    2. If position is past the end of input, then skip to the next step in the overall set of steps.

    3. Otherwise, if the character at position is a U+005A LATIN CAPITAL LETTER Z, then:

       1. Add the timezone corresponding to UTC (zero offset) to the results.

       2. Advance position to the next character in input.

       3. Skip to the next step in the overall set of steps.

    4. Otherwise, if the character at position is either a U+002B PLUS SIGN ("+") or a U+002D HYPHEN-MINUS ("-"), then:

       1. 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".

       2. Advance position to the next character in input.

       3. 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 the string is invalid.

       4. Interpret the sequence collected in the last step as a base ten number, and let that number be timezone_hours.

       5. If timezone_hours is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;timezone_hoursAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;23, then the string is invalid; abort these steps.
       6. If sign is "negative", then negate timezone_hours.

       7. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then the string is invalid; abort these steps. Otherwise, move position forwards one character.

       8. 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 the string is invalid.

       9. Interpret the sequence collected in the last step as a base ten number, and let that number be timezone_minutes.

       10. If timezone_minutes is not a number in the range 0AMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;timezone_minutesAMPERSANDnbsp;AMPERSANDle;AMPERSANDnbsp;59, then the string is invalid; abort these steps.

       11. Add the timezone corresponding to an offset of timezone_hours hours and timezone_minutes minutes to the results.

       12. Skip to the next step in the overall set of steps.

    5. Otherwise, the string is invalid; abort these steps.

21. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

22. If position is not past the end of input, then the string is invalid.

23. Abort these steps (the string is parsed).

3.2.4. Tokens

An unordered 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.

A string containing an unordered set of space-separated tokens may have leading or trailing space characters.

Thus, any string is a valid representation of an unordered set of space-separated tokens.

When a user agent has to split a string on spaces, it must use the following algorithm:

1. Let input be the string being parsed.

2. Let position be a pointer into input, initially pointing at the start of the string.

3. Let tokens be a list of tokens, initially empty.

4. Skip whitespace

5. While position is not past the end of input:

   1. Collect a sequence of characters that are not space characters.

   2. Add the string collected in the previous step to tokens.

   3. Skip whitespace

6. Return tokens.

When a user agent has to remove a token from a string, it must use the following algorithm:

1. Let input be the string being modified.

2. Let token be the token being removed. It will not contain any space characters.

3. Let output be the output string, initially empty.

4. Let position be a pointer into input, initially pointing at the start of the string.

5. If position is beyond the end of input, set the string being modified to output, and abort these steps.

6. If the character at position is a space character:

   1. Append the character at position to the end of output.

   2. Increment position so it points at the next character in input.

   3. Return to step 5 in the overall set of steps.

7. Otherwise, the character at position is the first character of a token. Collect a sequence of characters that are not space characters, and let that be s.

8. If s is exactly equal to token, then:

   1. Skip whitespace (in input).

   2. Remove any space characters currently at the end of output.

   3. 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.

9. Otherwise, append s to the end of output.

10. 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.

3.3. Documents and document fragments

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 only use elements, attributes, and attribute values for their appropriate semantic purposes.

AMPERSANDlt;!DOCTYPE htmlAMPERSANDgt;AMPERSANDlt;html lang="en-GB"AMPERSANDgt; AMPERSANDlt;headAMPERSANDgt; AMPERSANDlt;titleAMPERSANDgt; Demonstration AMPERSANDlt;/titleAMPERSANDgt; AMPERSANDlt;/headAMPERSANDgt; AMPERSANDlt;bodyAMPERSANDgt;  AMPERSANDlt;tableAMPERSANDgt;   AMPERSANDlt;trAMPERSANDgt; AMPERSANDlt;tdAMPERSANDgt; My favourite animal is the cat. AMPERSANDlt;/tdAMPERSANDgt; AMPERSANDlt;/trAMPERSANDgt;   AMPERSANDlt;trAMPERSANDgt;    AMPERSANDlt;tdAMPERSANDgt;     AMPERSANDmdash;AMPERSANDlt;a href="http://example.org/~ernest/"AMPERSANDgt;AMPERSANDlt;citeAMPERSANDgt;ErnestAMPERSANDlt;/citeAMPERSANDgt;AMPERSANDlt;/aAMPERSANDgt;,     in an essay from 1992    AMPERSANDlt;/tdAMPERSANDgt;   AMPERSANDlt;/trAMPERSANDgt;  AMPERSANDlt;/tableAMPERSANDgt; AMPERSANDlt;/bodyAMPERSANDgt;AMPERSANDlt;/htmlAMPERSANDgt;

AMPERSANDlt;!DOCTYPE htmlAMPERSANDgt;AMPERSANDlt;html lang="en-GB"AMPERSANDgt; AMPERSANDlt;headAMPERSANDgt; AMPERSANDlt;titleAMPERSANDgt; Demonstration AMPERSANDlt;/titleAMPERSANDgt; AMPERSANDlt;/headAMPERSANDgt; AMPERSANDlt;bodyAMPERSANDgt;  AMPERSANDlt;blockquoteAMPERSANDgt;   AMPERSANDlt;pAMPERSANDgt; My favourite animal is the cat. AMPERSANDlt;/pAMPERSANDgt;  AMPERSANDlt;/blockquoteAMPERSANDgt;  AMPERSANDlt;pAMPERSANDgt;   AMPERSANDmdash;AMPERSANDlt;a href="http://example.org/~ernest/"AMPERSANDgt;AMPERSANDlt;citeAMPERSANDgt;ErnestAMPERSANDlt;/citeAMPERSANDgt;AMPERSANDlt;/aAMPERSANDgt;,   in an essay from 1992  AMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;/bodyAMPERSANDgt;AMPERSANDlt;/htmlAMPERSANDgt;

AMPERSANDlt;bodyAMPERSANDgt; AMPERSANDlt;h1AMPERSANDgt;ABC CompanyAMPERSANDlt;/h1AMPERSANDgt; AMPERSANDlt;h2AMPERSANDgt;Leading the way in widget design since 1432AMPERSANDlt;/h2AMPERSANDgt; ...

AMPERSANDlt;bodyAMPERSANDgt; AMPERSANDlt;headerAMPERSANDgt;  AMPERSANDlt;h1AMPERSANDgt;ABC CompanyAMPERSANDlt;/h1AMPERSANDgt;  AMPERSANDlt;h2AMPERSANDgt;Leading the way in widget design since 1432AMPERSANDlt;/h2AMPERSANDgt; AMPERSANDlt;/headerAMPERSANDgt; ...

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. Structure

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. Authors must only put elements inside an element if that element allows them to be there according to its content model.

As noted in the conformance and terminology sections, for the purposes of determining if an element matches its content model or not, CDATASection nodes in the DOM are treated as equivalent to Text nodes, and entity reference nodes are treated as if they were expanded in place.

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 preceeded 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 only use elements in the HTML namespace in the contexts where they are allowed, as defined for each element. For XML compound documents, these contexts could be inside elements from other namespaces, if those elements are defined as providing the relevant contexts.

3.3.3. Kinds of elements

Each element in HTML falls into zero or more categories that group elements with similar characteristics together. This specification uses the following categories:

• Metadata elements
• Sectioning elements
• Block-level elements
• Strictly inline-level content
• Structured inline-level elements
• Interactive elements
• Form control elements

Some elements have unique requirements and do not fit into any particular category.

In addition, some elements represent various common concepts; for example, some elements represent paragraphs.

3.3.3.1. Block-level elements

Block-level elements are used for structural grouping of page content.

There are several kinds of block-level elements:

• Some can only contain other block-level elements: blockquote, section, article, header.
• Some can only contain inline-level content: p, h1-h6, address.
• Some can contain either block-level elements or inline-level content (but not both): nav, aside, footer, div.
• Finally, some have very specific content models: ul, ol, dl, table, script.

There are also elements that seem to be block-level but aren't, such as body, li, dt, dd, and td. These elements are allowed only in specific places, not simply anywhere that block-level elements are allowed.

Some block-level elements play multiple roles. For instance, the script elements is allowed inside head elements and can also be used as inline-level content. Similarly, the ul, ol, dl, table, and blockquote elements play dual roles as both block-level and inline-level elements.

3.3.3.2. Inline-level content

Inline-level content consists of text and various elements to annotate the text, as well as some embedded content (such as images or sound clips).

Inline-level content comes in various types:

Strictly inline-level content

Text, embedded content, and elements that annotate the text without introducing structural grouping. For example: a, meter, img. Elements used in contexts allowing only strictly inline-level content must not contain anything other than strictly inline-level content.

Structured inline-level elements

Block-level elements that can also be used as inline-level content. For example: ol, blockquote, table.

Some elements are defined to have as a content model significant inline content. This means that at least one descendant of the element must be significant text or embedded content.

Unless an element's content model explicitly states that it must contain significant inline content, simply having no text nodes and no elements satisfies an element whose content model is some kind of inline content.

Significant text, for the purposes of determining the presence of significant inline content, consists of any character other than those falling in the Unicode categories Zs, Zl, Zp, Cc, and Cf. [UNICODE]

AMPERSANDlt;pAMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;AMPERSANDlt;pAMPERSANDgt;AMPERSANDlt;emAMPERSANDgt;AMPERSANDamp;#x00A0;AMPERSANDlt;/emAMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;AMPERSANDlt;pAMPERSANDgt; AMPERSANDlt;olAMPERSANDgt;  AMPERSANDlt;liAMPERSANDgt;AMPERSANDlt;/liAMPERSANDgt; AMPERSANDlt;/olAMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;

Embedded content consists of elements that introduce content from other resources into the document, for example img. 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.

3.3.3.3. Determining if a particular element contains block-level elements or inline-level content

Some elements are defined to have content models that allow either block-level elements or inline-level content, but not both. For example, the aside and li elements.

To establish whether such an element is being used as a block-level container or as an inline-level container, for example in order to determine if a document conforms to these requirements, user agents must look at the element's child nodes. If any of the child nodes are not allowed in block-level contexts, then the element is being used for inline-level content. If all the child nodes are allowed in a block-level context, then the element is being used for block-level elements.

AMPERSANDlt;olAMPERSANDgt; AMPERSANDlt;liAMPERSANDgt;  AMPERSANDlt;pAMPERSANDgt; Hello World AMPERSANDlt;/pAMPERSANDgt;  AMPERSANDlt;styleAMPERSANDgt;   /* This example is illegal. */  AMPERSANDlt;/styleAMPERSANDgt; AMPERSANDlt;/liAMPERSANDgt;AMPERSANDlt;/olAMPERSANDgt;

AMPERSANDlt;asideAMPERSANDgt; AMPERSANDlt;olAMPERSANDgt;  AMPERSANDlt;liAMPERSANDgt; ... AMPERSANDlt;/liAMPERSANDgt; AMPERSANDlt;/olAMPERSANDgt; AMPERSANDlt;ulAMPERSANDgt;  AMPERSANDlt;liAMPERSANDgt; ... AMPERSANDlt;/liAMPERSANDgt; AMPERSANDlt;/ulAMPERSANDgt;AMPERSANDlt;/asideAMPERSANDgt;

AMPERSANDlt;asideAMPERSANDgt; AMPERSANDlt;olAMPERSANDgt;  AMPERSANDlt;liAMPERSANDgt; ... AMPERSANDlt;/liAMPERSANDgt; AMPERSANDlt;/olAMPERSANDgt; FooAMPERSANDlt;/asideAMPERSANDgt;

3.3.3.4. Interactive elements

Certain elements in HTML can be activated, for instance a elements, button elements, or input elements when their type attribute is set to radio. Activation of those elements can happen in various (UA-defined) ways, for instance via the mouse or keyboard.

When activation is performed via some method other than clicking the pointing device, the default action of the event that triggers the activation must, instead of being activating the element directly, be to fire a click event on the same element.

The default action of this click event, or of the real click event if the element was activated by clicking a pointing device, must be to dispatch yet another event, namely DOMActivate. It is the default action of that event that then performs the actual action.

For certain form controls, this process is complicated further by changes that must happen around the click event. [WF2]

Most interactive elements have content models that disallowed nesting interactive elements.

Need to define how default actions actually work. For instance, if you click an event inside a link, the event is triggered on that element, but then we'd like a click is sent on the link itself. So how does that happen? Does the link have a bubbling listener that triggers that second click event? what if there are multiple nested links, which one should we send that event to?

3.3.3.5. Paragraphs

A paragraph is typically 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.

Paragraphs can be represented by several elements. The address element always represents a paragraph of contact information for its section, the aside, nav, footer, li, and dd elements represent paragraphs with various specific semantics when they are used as inline-level content containers, the figure element represents a paragraph in the form of embedded content, and the p element represents all the other kinds of paragraphs, for which there are no dedicated elements.

3.4. Global attributes

The following attributes are common to and may be specified on all HTML elements (even those not defined in this specification):

Global attributes:

class

contenteditable

contextmenu

dir

draggable

id

lang

tabindex

title

In addition, the following event handler content attributes may be specified on any HTML element:

• onclick
• ...more events...

3.4.1. The id attribute

The id attribute represents its element's unique identifier. The value must be unique in the subtree within which the element finds itself and must contain at least one character.

If the value is not the empty string, user agents must associate the element with the given value (exactly) for the purposes of ID matching within the subtree the element finds itself (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.

3.4.2. 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 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.

Some elements, such as link and dfn, define additional semantics for the title attribute beyond the semantics described above.

The title DOM attribute must reflect the title content attribute.

3.4.3. The lang (HTML only) and xml:lang (XML only) attributes

The lang attribute 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]

The xml:lang attribute is defined in XML. [XML]

If these attributes are omitted from an element, then it implies that the language of this element is the same as the language of the parent element. Setting the attribute to the empty string indicates that the primary language is unknown.

The lang attribute may only be used on elements of HTML documents. Authors must not use the lang attribute in XML documents.

The xml:lang attribute may only be used on elements of XML documents. Authors must not use the xml:lang attribute in HTML documents.

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 or xml:lang attribute set. That specifies the language of the node.

If both the xml:lang attribute and the lang attribute are set on an element, user agents must use the xml:lang attribute, and the lang attribute must be ignored for the purposes of determining the element's language.

If no explicit language is given for the root element, 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).

User agents may use the element's language to determine proper processing or rendering (e.g. in the selection of appropriate fonts or pronounciations, or for dictionary selection).

The lang DOM attribute must reflect the lang content attribute.

3.4.4. The dir attribute

redefine this in terms of a microsyntax

The dir attribute specifies the element's text directionality. The attribute, if specified, must have either the literal value ltr or the literal value rtl.

If the attribute has the literal value ltr, the element's directionality is left-to-right. If the attribute has the literal value rtl, the element's directionality is right-to-left. If the attribute is omitted or has another value, then the directionality is unchanged.

The processing of this attribute depends on the presentation layer. For example, CSS 2.1 defines a mapping from this attribute to the CSS 'direction' and 'unicode-bidi' properties, and defines rendering in terms of those property.

The dir DOM attribute must reflect the dir content attribute.

3.4.5. Classes

Every HTML element may have a class attribute specified.

The attribute, if specified, must have a value that is an unordered set of space-separated tokens representing the various classes that the element belongs to.

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.

Assinging 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 predefined values defined in this specification where appropriate.

Classes that are not defined in this specification can be defined as extensions, as described below.

Authors should bear in mind that using the class attribute does not convey any additional meaning to the element unless the classes used have been defined by this specification or registered in the Wiki. There is no semantic difference between an element with a class attribute and one without. Authors that use classes that are not so defined should make sure, therefore, that their documents make as much sense once all class attributes have been removed as they do with the attributes present. User agents should not derive particular meanings from class attribute values that are neither defined by this specification nor registered in the Wiki.

The className DOM attribute must reflect the class content attribute.

3.4.5.1. Predefined class names

The following table summarises the class names that are defined by this specification. This table is non-normative; the actual definitions for the class names are given in the next few sections.

3.4.5.1.1. Class name "copyright"

The copyright class name indicates that the element contains the copyright for the document.

It must only be used on the following elements: p, span

3.4.5.1.2. Class name "error"

The error class name indicates that the element contains an error message, e.g. in an error message to the user in an interactive application, or an error notification in the report of a conformance checker.

It must only be used on the following elements: p, section, span, strong

It cannot be used on the body element; if the whole document is an error message then the appropriate metadata should be included at the network layer (e.g. with HTTP using the 4xx and 5xx status codes).

3.4.5.1.3. Class name "example"

The example class name indicates that the element contains some sample material or a worked example illustrating the neighboring content.

It must only be used on the following elements: aside, figure, p, span

3.4.5.1.4. Class name "issue"

The issue class name indicates that the element contains a point in dispute or a problem with the neighboring content that needs resolving. (Thus, this is typically only found in works-in-progress or drafts, not in completed documents.)

It must only be used on the following elements: aside, p, span

3.4.5.1.5. Class name "note"

The note class name indicates that the element contains an explanatory note or clarification.

It must only be used on the following elements: aside, p, span

3.4.5.1.6. Class name "search"

The search class name indicates that the element's primary purpose is to provide the user with an interface to perform a search (e.g. of the site's pages or of a database).

It must only be used on the following elements: aside, body, form, p, section, span

3.4.5.1.7. Class name "warning"

The warning class name indicates that the element contains a warning or admonition.

It must only be used on the following elements: article, aside, body, figure, p, section, span, strong

3.4.5.2. Other classes

Extensions to the predefined set of class keywords may be registered in the WHATWG Wiki ClassExtensions page.

Anyone is free to edit the WHATWG Wiki ClassExtensions page at any time to add a type. New classes must be specified with the following information:

Keyword

The actual class name being defined. The class name should not be confusingly similar to any other defined class name (e.g. differing only in case).

Applicable elements

A list of HTML elements to which the class applies, or one of the following values:

Metadata elements

Meaning any element described as being a metadata element.

Sectioning elements

Meaning any element described as being a sectioning element.

Block-level elements

Meaning any element described as being a block-level element, but only when that element is actually being used as a block-level element, and not, say, as a structured inline-level element.

Strictly inline-level elements

Meaning any element described as being strictly inline-level content.

Structured inline-level elements

Meaning any element described as being a structured inline-level element.

Interactive

Meaning any element described as being an interactive element.

Embedded content elements

Meaning any element described as being embedded content.

All elements

Meaning any element.

A document must not use a class defined in the Wiki on an element other than the elements that the Wiki says that class name is allowed on.

Brief description

A short description of what the keyword's meaning is.

Link to more details

A link to a more detailed description of the keyword's semantics and requirements. It could be another page on the Wiki, or a link to an external page.

Synonyms

A list of other keyword values that have exactly the same processing requirements. Authors should not use the values defined to be synonyms, they are only intended to allow user agents to support legacy content.

Status

One of the following:

Proposal

The keyword has not received wide peer review and approval. Someone has proposed it and is using it.

Accepted

The keyword has received wide peer review and approval. It has a specification that unambiguously defines how to handle pages that use the keyword, including when they use them in incorrect ways. Pages should use the keyword to mark up the semantic that it describes.

Unendorsed

The keyword has received wide peer review and it has been found wanting. Existing pages are using this keyword, but new pages should avoid it. The "brief description" and "link to more details" entries will give details of what authors should use instead.

If a keyword is added with the "proposal" status and found to be redundant with existing values, it should be removed and listed as a synonym for the existing value.

Conformance checkers must use the information given on the WHATWG Wiki ClassExtensions page to establish if a value not explicitly defined in this specification is defined, and if so, whether it is being used on the right elements. When an author uses a new class name not defined by either this specification or the Wiki page, conformance checkers may offer to add the value to the Wiki, with the details described above, with the "proposal" status.

This specification does not define how new values will get approved. It is expected that the Wiki will have a community that addresses this.

3.5. Interaction

3.5.1. Activation

The click() method must fire a click event at the element.

3.5.2. Focus

When an element is focused, key events received by the document must be targetted at that element. There is always an element focused; in the absence of other elements being focused, the document's root element is it.

Which element within a document currently has focus is independent of whether or not the document itself has the system focus.

Some focusable elements might take part in sequential focus navigation.

3.5.2.1. Focus management

The focus() and blur() methods must focus and unfocus the element respectively, if the element is focusable.

Well that clearly needs more.

The activeElement attribute must return the element in the document that has focus. If no element specifically has focus, this must return the root element.

The hasFocus attribute must return true if the document, one of its nested browsing contexts, or any element in the document or its browsing contexts currently has the system focus.

3.5.2.2. Sequential focus navigation

This section on the tabindex attribute needs to be checked for backwards-compatibility.

The tabindex attribute specifies the relative order of elements for the purposes of sequential focus navigation. The name "tab index" comes from the common use of the "tab" key to navigate through the focusable elements. The term "tabbing" refers to moving forward through the focusable elements.

The tabindex attribute, if specified, must have a value that is a valid integer.

If the attribute is specified, it must be parsed using the rules for parsing integers. If parsing the value returns an error, the attribute is ignored for the purposes of focus management (as if it wasn't specified).

A positive integer or zero specifies the index of the element in the current scope's tab order. Elements with the same index are sorted in tree order for the purposes of tabbing.

A negative integer specifies that the element should be removed from the tab order. If the element does normally take focus, it may still be focused using other means (e.g. it could be focused by a click).

If the attribute is absent (or invalid), then the user agent must treat the element as if it had the value 0 or the value -1, based on platform conventions.

For example, a user agent might default textarea elements to 0, and button elements to -1, making text fields part of the tabbing cycle but buttons not.

When an element that does not normally take focus (i.e. whose default value would be -1) has the tabindex attribute specified with a positive value, then it should be added to the tab order and should be made focusable. When focused, the element matches the CSS :focus pseudo-class and key events are dispatched on that element in response to keyboard input.

The tabIndex DOM attribute reflects the value of the tabIndex content attribute. If the attribute is not present (or has an invalid value) then the DOM attribute must return the UA's default value for that element, which will be either 0 (for elements in the tab order) or -1 (for elements not in the tab order).

3.6. The root element

3.6.1. The html element

Contexts in which this element may be used:

As the root element of a document.

Wherever a subdocument fragment is allowed in a compound document.

Content model:

A head element followed by a body element.

Element-specific attributes:

None (but see prose).

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The html element represents the root of an HTML document.

Though it has absolutely no effect and no meaning, the html element, in HTML documents, 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 the null 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 the null namespace specified.

3.7. Document metadata

Document metadata is represented by metadata elements in the document's head element.

3.7.1. The head element

Contexts in which this element may be used:

As the first element in an html element.

Content model:

In any order, exactly one title element, optionally one base element (HTML only), and zero or more other metadata elements (in particular, link, meta, style, and script).

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The head element collects the document's metadata.

3.7.2. The title element

Metadata element.

Contexts in which this element may be used:

In a head element containing no other title elements.

Content model:

Text (for details, see prose).

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The title element represents the document's title or name. Authors should use titles that identify their documents even when they are used out of context, for example in a user's history or bookmarks, or in search results. The document's title is often different from its first header, since the first header does not have to stand alone when taken out of context.

  AMPERSANDlt;title>Introduction to The Mating Rituals of BeesAMPERSANDlt;/title>    ...  AMPERSANDlt;h1>IntroductionAMPERSANDlt;/h1>  AMPERSANDlt;p>This companion guide to the highly successful  AMPERSANDlt;cite>Introduction to Medieval Bee-KeepingAMPERSANDlt;/cite> book is...

  AMPERSANDlt;title>Dances used during bee mating ritualsAMPERSANDlt;/title>    ...  AMPERSANDlt;h1>The DancesAMPERSANDlt;/h1>

The title element must not contain any elements.

The string to use as the document's title is given by the document.title DOM attribute. User agents should use the document's title when referring to the document in their user interface.

3.7.3. The base element

Metadata element.

Contexts in which this element may be used:

In a head element, before any elements that use relative URIs, and only if there are no other base elements anywhere in the document. Only in HTML documents (never in XML documents).

Content model:

Empty.

Element-specific attributes:

href

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLBaseElement : HTMLElement {           attribute DOMString href;};

The base element allows authors to specify the document's base URI for the purposes of resolving relative URIs.

The href content attribute, if specified, must contain a URI (or IRI).

User agents must use the value of the href attribute on the first base element in the document as the document entity's base URI for the purposes of section 5.1.1 of RFC 2396 ("Establishing a Base URI": "Base URI within Document Content"). [RFC2396] Note that this base URI from RFC 2396 is referred to by the algorithm given in XML Base, which is a normative part of this specification.

If the base URI given by this attribute is a relative URI, it must be resolved relative to the higher-level base URIs (i.e. the base URI from the encapsulating entity or the URI used to retrieve the entity) to obtain an absolute base URI.

The href content attribute must be reflected by the DOM href attribute.

Authors must not use the base element in XML documents. Authors should instead use the xml:base attribute. [XMLBASE]

3.7.4. The link element

Metadata element.

Contexts in which this element may be used:

In a head element.

Content model:

Empty.

Element-specific attributes:

href (required)

rel (required)

media

hreflang

type

Also, the title attribute has special semantics on this element.

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLLinkElement : HTMLElement {           attribute boolean disabled;           attribute DOMString href;           attribute DOMString rel;           attribute DOMString media;           attribute DOMString hreflang;           attribute DOMString type;};

The LinkStyle interface defined in DOM2 Style must also be implemented by this element. [DOM2STYLE]

The link element allows authors to indicate explicit relationships between their document and other resources.

The destination of the link is given by the href attribute, which must be present and must contain a URI (or IRI). If the href attribute is absent, then the element does not define a link.

The type of link indicated (the relationship) is given by the value of the rel attribute, which must be present. The allowed values and their meanings are defined in a later section. If the rel attribute is absent, or if the value used is not allowed according to the definitions in this specification, then the element does not define a link.

Two categories of links can be created using the link element. Links to external resources are links to resources that are to be used to augment the current document, and hyperlink links are links to other documents. The link types section defines whether a particular link type is an external resource or a hyperlink. One element can create multiple links (of which some might be external resource links and some might be hyperlinks). User agents should process the links on a per-link basis, not a per-element basis.

The exact behaviour for links to external resources depends on the exact relationship, as defined for the relevant link type. Some of the attributes control whether or not the external resource is to be applied (as defined below). For external resources that are represented in the DOM (for example, style sheets), the DOM representation must be made available even if the resource is not applied. (However, user agents may opt to only fetch such resources when they are needed, instead of pro-actively downloading all the external resources that are not applied.)

Interactive user agents should provide users with a means to follow the hyperlinks created using the link element, somewhere within their user interface. The exact interface is not defined by this specification, but it should include the following information (obtained from the element's attributes, again as defined below), in some form or another (possibly simplified), for each hyperlink created with each link element in the document:

• The relationship between this document and the resource (given by the rel attribute)
• The title of the resource (given by the title attribute).
• The URI of the resource (given by the href attribute).
• The language of the resource (given by the hreflang attribute).
• The optimum media for the resource (given by the media attribute).

User agents may also include other information, such as the type of the resource (as given by the type attribute).

The media attribute says which media the resource applies to. The value must be a valid media query. [MQ]

If the link is a hyperlink then the media attribute is purely advisory, and describes for which media the document in question was designed.

However, if the link is an external resource link, then the media attribute is prescriptive. The user agent must only apply the external resource to views while their state match the listed media.

The default, if the media attribute is omitted, is all, meaning that by default links apply to all media.

The hreflang attribute on the link element has the same semantics as the hreflang attribute on hyperlink elements.

The type attribute gives the MIME type of the linked resource. It is purely advisory. The value must be a valid MIME type, optionally with parameters. [RFC2046]

For external resource links, user agents may use the type given in this attribute to decide whether or not to consider using the resource at all. If the UA does not support the given MIME type for the given link relationship, then the UA may opt not to download and apply the resource.

User agents must not consider the type attribute authoritative AMPERSANDmdash; upon fetching the resource, user agents must only use the Content-Type information associated with the resource to determine its type, not metadata included in the link to the resource.

If the attribute is omitted, then the UA must fetch the resource to determine its type and thus determine if it supports (and can apply) that external resource.

AMPERSANDlt;link rel="stylesheet" href="A" type="text/css"AMPERSANDgt;AMPERSANDlt;link rel="stylesheet" href="B" type="text/plain"AMPERSANDgt;AMPERSANDlt;link rel="stylesheet" href="C"AMPERSANDgt;

The title attribute gives the title of the link. With one exception, it is purely advisory. The value is text. The exception is for style sheet links, where the title attribute defines alternate style sheet sets.

The title attribute on link elements differs from the global title attribute of most other elements in that a link without a title does not inherit the title of the parent element: it merely has no title.

Some versions of HTTP defined a Link: header, to be processed like a series of link elements. When processing links, those must be taken into consideration as well. For the purposes of ordering, links defined by HTTP headers must be assumed to come before any links in the document, in the order that they were given in the HTTP entity header. Relative URIs in these headers must be resolved according to the rules given in HTTP, not relative to base URIs set by the document (e.g. using a base element or xml:base attributes). [RFC2616] [RFC2068]

The DOM attributes href, rel, media, hreflang, and type each must reflect the respective content attributes of the same name.

The DOM attribute disabled only applies to style sheet links. When the link element defines a style sheet link, then the disabled attribute behaves as defined for the alternate style sheets DOM. For all other link elements it must always return false and must do nothing on setting.

3.7.5. The meta element

Metadata element.

Contexts in which this element may be used:

In a head element.

Content model:

Empty.

Element-specific attributes:

name

http-equiv (HTML only, optional)

content

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLMetaElement : HTMLElement {           attribute DOMString content;           attribute DOMString name;};

The meta element allows authors to specify document metadata that cannot be expressed using the title, base, link, style, and script elements. The metadata is expressed in terms of name/value pairs: the name attribute on the meta element gives the name, and the content attribute on the same element gives the value.

If a meta element has no name attribute, it does not set document metadata. If a meta element has no content attribute, then the value part of the metadata name/value pair is the empty string.

The value must not be a URI. Links must be represented using the link element, not the meta element.

The DOM attributes name and content must reflect the respective content attributes of the same name.

3.7.5.1. Standard metadata names

This specification defines a few names for the name attribute of the meta element.

generator

The value must be a free-form string that identifies the software used to generate the document. This value must not be used on hand-authored pages.

3.7.5.2. Other metadata names

Extensions to the predefined set of metadata names may be registered in the WHATWG Wiki MetaExtensions page.

Anyone is free to edit the WHATWG Wiki MetaExtensions page at any time to add a type. These new names must be specified with the following information:

Keyword

The actual name being defined. The name should not be confusingly similar to any other defined name (e.g. differing only in case).

Brief description

A short description of what the metadata name's meaning is, including the format the value is required to be in.

Link to more details

A link to a more detailed description of the metadata name's semantics and requirements. It could be another page on the Wiki, or a link to an external page.

Synonyms

A list of other names that have exactly the same processing requirements. Authors should not use the names defined to be synonyms, they are only intended to allow user agents to support legacy content.

Status

One of the following:

Proposal

The name has not received wide peer review and approval. Someone has proposed it and is using it.

Accepted

The name has received wide peer review and approval. It has a specification that unambiguously defines how to handle pages that use the name, including when they use it in incorrect ways.

Unendorsed

The metadata name has received wide peer review and it has been found wanting. Existing pages are using this keyword, but new pages should avoid it. The "brief description" and "link to more details" entries will give details of what authors should use instead, if anything.

If a metadata name is added with the "proposal" status and found to be redundant with existing values, it should be removed and listed as a synonym for the existing value.

Conformance checkers must use the information given on the WHATWG Wiki MetaExtensions page to establish if a value not explicitly defined in this specification is allowed or not. When an author uses a new type not defined by either this specification or the Wiki page, conformance checkers should offer to add the value to the Wiki, with the details described above, with the "proposal" status.

This specification does not define how new values will get approved. It is expected that the Wiki will have a community that addresses this.

3.7.5.3. Specifying and establishing the document's character encoding

The meta element may also be used, in HTML only (not in XHTML) to provide UAs with character encoding information for the file. To do this, the meta element must be the first element in the head element, it must have the http-equiv attribute set to the literal value Content-Type, and must have the content attribute set to the literal value text/html; charset= immediately followed by the character encoding, which must be a valid character encoding name. [IANACHARSET] When the meta element is used in this way, there must be no other attributes set on the element, and the http-equiv attribute must be listed first in the source. Other than for giving the document's character encoding in this way, the http-equiv attribute must not be used.

We should allow those strings to be case-insensitive, and for zero-or-more spaces where we currently require just one.

In XHTML, the XML declaration should be used for inline character encoding information, if necessary.

Authors should avoid including inline character encoding information. Character encoding information should instead be included at the transport level (e.g. using the HTTP Content-Type header).

3.7.6. The style element

Metadata element.

Contexts in which this element may be used:

In a head element.

Content model:

Depends on the value of the type attribute.

Element-specific attributes:

media

type

Also, the title attribute has special semantics on this element.

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLStyleElement : HTMLElement {           attribute boolean disabled;           attribute DOMString media;           attribute DOMString type;};

The LinkStyle interface defined in DOM2 Style must also be implemented by this element. [DOM2STYLE]

The style element allows authors to embed style information in their documents.

If the type attribute is given, it must contain a MIME type, optionally with parameters, that designates a styling language. [RFC2046] If the attribute is absent, the type defaults to text/css. [RFC2138]

If the UA supports the given styling language, then the UA must use the given styles as appropriate for that language.

When examining types to determine if they support the language, user agents must not ignore unknown MIME parameters AMPERSANDmdash; types with unknown parameters must be assumed to be unsupported.

The media attribute says which media the styles apply to. The value must be a valid media query. [MQ] User agents must only apply the styles to views while their state match the listed media.

The default, if the media attribute is omitted, is all, meaning that by default styles apply to all media.

The title attribute on style elements defines alternate style sheet sets. If the style element has no title attribute, then it has no title; the title attribute of ancestors does not apply to the style element.

The title attribute on style elements, like the title attribute on link elements, differs from the global title attribute in that a style block without a title does not inherit the title of the parent element: it merely has no title.

All descendant elements must be processed, according to their semantics, before the style element itself is evaluated. For styling languages that consist of pure text, user agents must evaluate style elements by passing the concatenation of the contents of all the text nodes that are direct children of the style element (not any other nodes such as comments or elements), in tree order, to the style system. For XML-based styling languages, user agents must pass all the children nodes of the style element to the style system.

This specification does not specify a style system, but CSS is expected to be supported by most Web browsers. [CSS21]

The DOM attributes media and type each must reflect the respective content attributes of the same name.

The DOM disabled attribute behaves as defined for the alternate style sheets DOM.

3.8. Sections

Sectioning elements are elements that divide the page into, for lack of a better word, sections. This section describes HTML's sectioning elements and elements that support them.

Some elements are scoped to their nearest ancestor sectioning element. For example, address elements apply just to their section. For such elements x, the elements that apply to a sectioning element e are all the x elements whose nearest sectioning element is e.

3.8.1. The body element

Sectioning element.

Contexts in which this element may be used:

As the second element in an html element.

Content model:

Zero or more block-level elements.

Element-specific attributes:

None.

Predefined classes that apply to this element:

search, warning

DOM interface:

No difference from HTMLElement.

The body element represents the main content of the document.

The body element potentially has a heading. See the section on headings and sections for further details.

In conforming documents, there is only one body element. The document.body DOM attribute provides scripts with easy access to a document's body element.

Some DOM operations (for example, parts of the drag and drop model) are defined in terms of "the body element". This refers to a particular element in the DOM, as per the definition of the term, and not any arbitrary body element.

3.8.2. The section element

Sectioning block-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Content model:

Zero or more block-level elements.

Element-specific attributes:

None.

Predefined classes that apply to this element:

error, example, search, warning

DOM interface:

No difference from HTMLElement.

The section element represents a generic document or application section. A section, in this context, is a thematic grouping of content, typically with a header, possibly with a footer.

Examples of sections would be chapters, the various tabbed pages in a tabbed dialog box, or the numbered sections of a thesis. A Web site's home page could be split into sections for an introduction, news items, contact information.

Each section element potentially has a heading. See the section on headings and sections for further details.

3.8.3. The nav element

Sectioning block-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Content model:

Zero or more block-level elements, or inline-level content (but not both).

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The nav element represents a section of a page that links to other pages or to parts within the page: a section with navigation links.

When used as an inline-level content container, the element represents a paragraph.

Each nav element potentially has a heading. See the section on headings and sections for further details.

3.8.4. The article element

Sectioning block-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Content model:

Zero or more block-level elements.

Element-specific attributes:

None.

Predefined classes that apply to this element:

warning

DOM interface:

No difference from HTMLElement.

The article element represents a section of a page that consists of a composition that forms an independent part of a document, page, or site. This could be a forum post, a magazine or newspaper article, a Web log entry, a user-submitted comment, or any other independent item of content.

An article element is "independent" in that its contents could stand alone, for example in syndication. However, the element is still associated with its ancestors; for instance, contact information that applies to a parent body element still covers the article as well.

When article elements are nested, the inner article elements represent articles that are in principle related to the contents of the outer article. For instance, a Web log entry on a site that accepts user-submitted comments could represent the comments as article elements nested within the article element for the Web log entry.

Author information associated with an article element (q.v. the address element) does not apply to nested article elements.

Each article element potentially has a heading. See the section on headings and sections for further details.

3.8.5. The blockquote element

Sectioning block-level element, and structured inline-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Where structured inline-level elements are allowed.

Content model:

Zero or more block-level elements.

Element-specific attributes:

cite

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLQuoteElement : HTMLElement {           attribute DOMString cite;};

The HTMLQuoteElement interface is also used by the q element.

The blockquote element represents a section that is quoted from another source.

Content inside a blockquote must be quoted from another source, whose URI, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a URI (or IRI). User agents should allow users to follow such citation links.

If a blockquote element is preceeded or followed by a p element that contains a single cite element and is itself not preceeded or followed by another blockquote element and does not itself have a q element descendant, then, the citation given by that cite element gives the source of the quotation contained in the blockquote element.

Each blockquote element potentially has a heading. See the section on headings and sections for further details.

The cite DOM attribute reflects the element's cite content attribte.

The best way to represent a conversation is not with the cite and blockquote elements, but with the dialog element.

3.8.6. The aside element

Sectioning block-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Content model:

Zero or more block-level elements, or inline-level content (but not both).

Element-specific attributes:

None.

Predefined classes that apply to this element:

example, issue, note, search, warning

DOM interface:

No difference from HTMLElement.

The aside element represents a section of a page that consists of content that is tangentially related to the content around the aside element, and which could be considered separate from that content. Such sections are often represented as sidebars in printed typography.

When used as an inline-level content container, the element represents a paragraph.

Each aside element potentially has a heading. See the section on headings and sections for further details.

3.8.7. The h1, h2, h3, h4, h5, and h6 elements

Block-level elements.

Contexts in which these elements may be used:

Where block-level elements are expected.

Content model:

Significant strictly inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

These elements define headers for their sections.

The semantics and meaning of these elements are defined in the section on headings and sections.

These elements have a rank given by the number in their name. The h1 element is said to have the highest rank, the h6 element has the lowest rank, and two elements with the same name have equal rank.

These elements must not be empty.

3.8.8. The header element

Block-level element.

Contexts in which this element may be used:

Where block-level elements are expected and there are no header ancestors.

Content model:

Zero or more block-level elements, including at least one descendant h1, h2, h3, h4, h5, or h6 element, but no sectioning element descendants, no header element descendants, and no footer element descendants.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The header element represents the header of a section. Headers may contain more than just the section's heading AMPERSANDmdash; for example it would be reasonable for the header to include version history information.

header elements must not contain any header elements, footer elements, or any sectioning elements (such as section) as descendants.

header elements must have at least one h1, h2, h3, h4, h5, or h6 element as a descendant.

For the purposes of document summaries, outlines, and the like, header elements are equivalent to the highest ranked h1-h6 element descendant (the first such element if there are multiple elements with that rank).

Other heading elements indicate subheadings or subtitles.

AMPERSANDlt;headerAMPERSANDgt; AMPERSANDlt;h1AMPERSANDgt;The reality dysfunctionAMPERSANDlt;/h1AMPERSANDgt; AMPERSANDlt;h2AMPERSANDgt;Space is not the only voidAMPERSANDlt;/h2AMPERSANDgt;AMPERSANDlt;/headerAMPERSANDgt;

AMPERSANDlt;headerAMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;Welcome to...AMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;h1AMPERSANDgt;Voidwars!AMPERSANDlt;/h1AMPERSANDgt;AMPERSANDlt;/headerAMPERSANDgt;

AMPERSANDlt;headerAMPERSANDgt; AMPERSANDlt;h1AMPERSANDgt;Scalable Vector Graphics (SVG) 1.2AMPERSANDlt;/h1AMPERSANDgt; AMPERSANDlt;h2AMPERSANDgt;W3C Working Draft 27 October 2004AMPERSANDlt;/h2AMPERSANDgt; AMPERSANDlt;dlAMPERSANDgt;  AMPERSANDlt;dtAMPERSANDgt;This version:AMPERSANDlt;/dtAMPERSANDgt;  AMPERSANDlt;ddAMPERSANDgt;AMPERSANDlt;a href="http://www.w3.org/TR/2004/WD-SVG12-20041027/"AMPERSANDgt;http://www.w3.org/TR/2004/WD-SVG12-20041027/AMPERSANDlt;/aAMPERSANDgt;AMPERSANDlt;/ddAMPERSANDgt;  AMPERSANDlt;dtAMPERSANDgt;Previous version:AMPERSANDlt;/dtAMPERSANDgt;  AMPERSANDlt;ddAMPERSANDgt;AMPERSANDlt;a href="http://www.w3.org/TR/2004/WD-SVG12-20040510/"AMPERSANDgt;http://www.w3.org/TR/2004/WD-SVG12-20040510/AMPERSANDlt;/aAMPERSANDgt;AMPERSANDlt;/ddAMPERSANDgt;  AMPERSANDlt;dtAMPERSANDgt;Latest version of SVG 1.2:AMPERSANDlt;/dtAMPERSANDgt;  AMPERSANDlt;ddAMPERSANDgt;AMPERSANDlt;a href="http://www.w3.org/TR/SVG12/"AMPERSANDgt;http://www.w3.org/TR/SVG12/AMPERSANDlt;/aAMPERSANDgt;AMPERSANDlt;/ddAMPERSANDgt;  AMPERSANDlt;dtAMPERSANDgt;Latest SVG Recommendation:AMPERSANDlt;/dtAMPERSANDgt;  AMPERSANDlt;ddAMPERSANDgt;AMPERSANDlt;a href="http://www.w3.org/TR/SVG/"AMPERSANDgt;http://www.w3.org/TR/SVG/AMPERSANDlt;/aAMPERSANDgt;AMPERSANDlt;/ddAMPERSANDgt;  AMPERSANDlt;dtAMPERSANDgt;Editor:AMPERSANDlt;/dtAMPERSANDgt;  AMPERSANDlt;ddAMPERSANDgt;Dean Jackson, W3C, AMPERSANDlt;a href="mailto:dean@w3.org"AMPERSANDgt;dean@w3.orgAMPERSANDlt;/aAMPERSANDgt;AMPERSANDlt;/ddAMPERSANDgt;  AMPERSANDlt;dtAMPERSANDgt;Authors:AMPERSANDlt;/dtAMPERSANDgt;  AMPERSANDlt;ddAMPERSANDgt;See AMPERSANDlt;a href="#authors"AMPERSANDgt;Author ListAMPERSANDlt;/aAMPERSANDgt;AMPERSANDlt;/ddAMPERSANDgt; AMPERSANDlt;/dlAMPERSANDgt; AMPERSANDlt;p class="copyright"AMPERSANDgt;AMPERSANDlt;a href="http://www.w3.org/Consortium/Legal/ipr-notic ...AMPERSANDlt;/headerAMPERSANDgt;

The section on headings and sections defines how header elements are assigned to individual sections.

The rank of a header element is the same as for an h1 element (the highest rank).

3.8.9. The footer element

Block-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Content model:

Either zero or more block-level elements, but with no h1, h2, h3, h4, h5, h6, header, or footer elements as descendants, and with no sectioning elements as descendants; or, inline-level content (but not both).

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The footer element represents the footer for the section it applies to. A footer typically contains information about its section such as who wrote it, links to related documents, copyright data, and the like.

footer elements must not contain any footer, header, h1, h2, h3, h4, h5, or h6 elements, or any of the sectioning elements (such as section), as descendants.

When used as an inline-level content container, the element represents a paragraph.

Contact information for the section given in a footer should be marked up using the address element.

3.8.10. The address element

Block-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Content model:

Inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The address element represents a paragraph of contact information for the section it applies to.

AMPERSANDlt;ADDRESS> AMPERSANDlt;A href="../People/Raggett/">Dave RaggettAMPERSANDlt;/A>,  AMPERSANDlt;A href="../People/Arnaud/">Arnaud Le HorsAMPERSANDlt;/A>,  contact persons for the AMPERSANDlt;A href="Activity">W3C HTML ActivityAMPERSANDlt;/A>AMPERSANDlt;/ADDRESS>

The address element must not be used to represent arbitrary addresses (e.g. postal addresses), unless those addresses are contact information for the section. (The p element is the appropriate element for marking up such addresses.)

The address element must not contain information other than contact information.

AMPERSANDlt;ADDRESS>Last Modified: 1999/12/24 23:37:50AMPERSANDlt;/ADDRESS>

Typically, the address element would be included with other information in a footer element.

To determine the contact information for a sectioning element (such as a document's body element, which would give the contact information for the page), UAs must collect all the address elements that apply to that sectioning element and its ancestor sectioning elements. The contact information is the collection of all the information given by those elements.

Contact information for one sectioning element, e.g. a aside element, does not apply to its ancestor elements, e.g. the page's body.

3.8.11. Headings and sections

The h1-h6 elements and the header element are headings.

The first heading in a sectioning element gives the header for that section. Subsequent headers of equal or higher rank start new (implied) sections, headers of lower rank start subsections that are part of the previous one.

Sectioning elements other than blockquote are always considered subsections of their nearest ancestor sectioning element, regardless of what implied sections other headings may have created. However, blockquote elements are associated with implied sections. Effectively, blockquote elements act like sections on the inside, and act opaquely on the outside.

AMPERSANDlt;bodyAMPERSANDgt; AMPERSANDlt;h1AMPERSANDgt;FooAMPERSANDlt;/h1AMPERSANDgt; AMPERSANDlt;h2AMPERSANDgt;BarAMPERSANDlt;/h2AMPERSANDgt; AMPERSANDlt;blockquoteAMPERSANDgt;  AMPERSANDlt;h3AMPERSANDgt;BlaAMPERSANDlt;/h3AMPERSANDgt; AMPERSANDlt;/blockquoteAMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;BazAMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;h2AMPERSANDgt;QuuxAMPERSANDlt;/h2AMPERSANDgt; AMPERSANDlt;sectionAMPERSANDgt;  AMPERSANDlt;h3AMPERSANDgt;ThudAMPERSANDlt;/h3AMPERSANDgt; AMPERSANDlt;/sectionAMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;GruntAMPERSANDlt;/pAMPERSANDgt;AMPERSANDlt;/bodyAMPERSANDgt;

Sections may contain headers of any rank, but authors are strongly encouraged to either use only h1 elements, or to use elements of the appropriate rank for the section's nesting level.

Authors are also encouraged to explictly wrap sections in sectioning elements, instead of relying on the implicit sections generated by having multiple heading in one sectioning element.

AMPERSANDlt;bodyAMPERSANDgt; AMPERSANDlt;h4AMPERSANDgt;ApplesAMPERSANDlt;/h4AMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;Apples are fruit.AMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;sectionAMPERSANDgt;  AMPERSANDlt;h2AMPERSANDgt;TasteAMPERSANDlt;/h2AMPERSANDgt;  AMPERSANDlt;pAMPERSANDgt;They taste lovely.AMPERSANDlt;/pAMPERSANDgt;  AMPERSANDlt;h6AMPERSANDgt;SweetAMPERSANDlt;/h6AMPERSANDgt;  AMPERSANDlt;pAMPERSANDgt;Red apples are sweeter than green ones.AMPERSANDlt;/pAMPERSANDgt;  AMPERSANDlt;h1AMPERSANDgt;ColorAMPERSANDlt;/h1AMPERSANDgt;  AMPERSANDlt;pAMPERSANDgt;Apples come in various colors.AMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;/sectionAMPERSANDgt;AMPERSANDlt;/bodyAMPERSANDgt;

AMPERSANDlt;bodyAMPERSANDgt; AMPERSANDlt;h1AMPERSANDgt;ApplesAMPERSANDlt;/h1AMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;Apples are fruit.AMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;sectionAMPERSANDgt;  AMPERSANDlt;h2AMPERSANDgt;TasteAMPERSANDlt;/h2AMPERSANDgt;  AMPERSANDlt;pAMPERSANDgt;They taste lovely.AMPERSANDlt;/pAMPERSANDgt;  AMPERSANDlt;sectionAMPERSANDgt;   AMPERSANDlt;h3AMPERSANDgt;SweetAMPERSANDlt;/h3AMPERSANDgt;   AMPERSANDlt;pAMPERSANDgt;Red apples are sweeter than green ones.AMPERSANDlt;/pAMPERSANDgt;  AMPERSANDlt;/sectionAMPERSANDgt; AMPERSANDlt;/sectionAMPERSANDgt; AMPERSANDlt;sectionAMPERSANDgt;  AMPERSANDlt;h2AMPERSANDgt;ColorAMPERSANDlt;/h2AMPERSANDgt;  AMPERSANDlt;pAMPERSANDgt;Apples come in various colors.AMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;/sectionAMPERSANDgt;AMPERSANDlt;/bodyAMPERSANDgt;

3.8.11.1. Creating an outline

Documents can be viewed as a tree of sections, which defines how each element in the tree is semantically related to the others, in terms of the overall section structure. This tree is related to the document tree, but there is not a one-to-one relationship between elements in the DOM and the document's sections.

The tree of sections should be used when generating document outlines, for example when generating tables of contents.

To derive the tree of sections from the document tree, a hypothetical tree is used, consisting of a view of the document tree containing only the h1-h6 and header elements, and the sectioning elements other than blockquote. Descendants of h1-h6, header, and blockquote elements must be removed from this view.

The hypothetical tree must be rooted at the root element or at a sectioning element. In particular, while the sections inside blockquotes do not contribute to the document's tree of sections, blockquotes can have outlines of their own.

UAs must take this hypothetical tree (which will become the outline) and mutate it by walking it depth first in tree order and, for each h1-h6 or header element that is not the first element of its parent sectioning element, inserting a new sectioning element, as follows:

If the element is a header element, or if it is an h1-h6 node of rank equal to or higher than the first element in the parent sectioning element (assuming that is also an h1-h6 node), or if the first element of the parent sectioning element is a sectioning element:

Insert the new sectioning element as the immediately following sibling of the parent sectioning element, and move all the elements from the current heading element up to the end of the parent sectioning element into the new sectioning element.

Otherwise:

Move the current heading element, and all subsequent siblings up to but excluding the next sectioning element, header element, or h1-h6 of equal or higher rank, whichever comes first, into the new sectioning element, then insert the new sectioning element where the current header was.

The outline is then the resulting hypothetical tree. The ranks of the headers become irrelevant at this point: each sectioning element in the hypothetical tree contains either no or one heading element child. If there is one, then it gives the section's heading, of there isn't, the section has no heading.

Sections are nested as in the hypothetical tree. If a sectioning element is a child of another, that means it is a subsection of that other section.

When creating an interactive table of contents, entries should jump the user to the relevant section element, if it was a real element in the original document, or to the heading, if the section element was one of those created during the above process.

Selecting the first section of the document therefore always takes the user to the top of the document, regardless of where the first header in the body is to be found.

function (n) {  // This implementation only knows about HTML elements.  // An implementation that supports other languages might be  // different.  // Reject anything that isn't an element.  if (n.nodeType != Node.ELEMENT_NODE)    return NodeFilter.FILTER_REJECT;  // Skip any descendants of headings.  if (n.parentNode AMPERSANDAMPERSAND n.parentNode.namespaceURI == 'http://www.w3.org/1999/xhtml') AMPERSANDAMPERSAND      (n.parentNode.localName == 'h1' || n.parentNode.localName == 'h2' ||       n.parentNode.localName == 'h3' || n.parentNode.localName == 'h4' ||       n.parentNode.localName == 'h5' || n.parentNode.localName == 'h6' ||       n.parentNode.localName == 'header')    return NodeFilter.FILTER_REJECT;  // Skip any blockquotes.  if (n.namespaceURI == 'http://www.w3.org/1999/xhtml') AMPERSANDAMPERSAND      (n.localName == 'blockquote'))    return NodeFilter.FILTER_REJECT;  // Accept HTML elements in the list given in the prose above.  if ((n.namespaceURI == 'http://www.w3.org/1999/xhtml') AMPERSANDAMPERSAND      (n.localName == 'body' || /*n.localName == 'blockquote' ||*/       n.localName == 'section' || n.localName == 'nav' ||       n.localName == 'article' || n.localName == 'aside' ||       n.localName == 'h1' || n.localName == 'h2' ||       n.localName == 'h3' || n.localName == 'h4' ||       n.localName == 'h5' || n.localName == 'h6' ||       n.localName == 'header'))    return NodeFilter.FILTER_ACCEPT;  // Skip the rest.  return NodeFilter.FILTER_SKIP;}

3.8.11.2. Determining which heading and section applies to a particular node

Given a particular node, user agents must use the following algorithm, in the given order, to determine which heading and section the node is most closely associated with. The processing of this algorithm must stop as soon as the associated section and heading are established (even if they are established to be nothing).

1. If the node has an ancestor that is a header element, then the associated heading is the most distant such ancestor. The associated section is that header's associated section (i.e. repeat this algorithm for that header).
2. If the node has an ancestor that is an h1-h6 element, then the associated heading is the most distant such ancestor. The associated section is that heading's section (i.e. repeat this algorithm for that heading element).
3. If the node is an h1-h6 element or a header element, then the associated heading is the element itself. The UA must then generate the hypothetical section tree described in the previous section, rooted at the nearest section ancestor (or the root element if there is no such ancestor). If the parent of the heading in that hypothetical tree is an element in the real document tree, then that element is the associated section. Otherwise, there is no associated section element.
4. If the node is a sectioning element, then the associated section is itself. The UA must then generate the hypothetical section tree described in the previous section, rooted at the section itself. If the section element, in that hypothetical tree, has a child element that is an h1-h6 element or a header element, then that element is the associated heading. Otherwise, there is no associated heading element.
5. If the node is a footer or address element, then the associated section is the nearest ancestor sectioning element, if there is one. The node's associated heading is the same as that sectioning element's associated heading (i.e. repeat this algorithm for that sectioning element). If there is no ancestor sectioning element, the element has no associated section nor an associated heading.
6. Otherwise, the node is just a normal node, and the document has to be examined more closely to determine its section and heading. Create a view rooted at the nearest ancestor sectioning element (or the root element if there is none) that has just h1-h6 elements, header elements, the node itself, and sectioning elements other than blockquote elements. (Descendants of any of the nodes in this view can be ignored, as can any node later in the tree than the node in question, as the algorithm below merely walks backwards up this view.)
7. Let n be an iterator for this view, initialised at the node in question.
8. Let c be the current best candidate heading, initially null, and initially not used. It is used when top-level heading candidates are to be searched for (see below).
9. Repeat these steps (which effectively goes backwards through the node's previous siblings) until an answer is found:
   1. If n points to a node with no previous sibling, and c is null, then return the node's parent node as the answer. If the node has no parent node, return null as the answer.
   2. Otherwise, if n points to a node with no previous sibling, return c as the answer.
   3. Adjust n so that it points to the previous sibling of the current position.
   4. If n is pointing at an h1 or header element, then return that element as the answer.
   5. If n is pointing at an h2-h6 element, and heading candidates are not being searched for, then return that element as the answer.
   6. Otherwise, if n is pointing at an h2-h6 element, and either c is still null, or c is a heading of lower rank than this one, then set c to be this element, and continue going backwards through the previous siblings.
   7. If n is pointing at a sectioning element, then from this point on top-level heading candidates are being searched for. (Specifically, we are looking for the nearest top-level header for the current section.) Continue going backwards through the previous siblings.
10. If the answer from the previous step (the loop) is null, which can only happen if the node has no preceeding headings and is not contained in a sectioning element, then there is no associated heading and no associated section.
11. Otherwise, if the answer from the earlier loop step is a sectioning element, then the associated section is that element and the associated heading is that sectioning element's associated heading (i.e. repeat this algorithm for that section).
12. Otherwise, if the answer from that same earlier step is an h1-h6 element or a header element, then the associated heading is that element and the associated section is that heading element's associated section (i.e. repeat this algorithm for that heading).

Not all nodes have an associated header or section. For example, if a section is implied, as when multiple headers are found in one sectioning element, then a node in that section has an anonymous associated section (its section is not represented by a real element), and the algorithm above does not associate that node with any particular sectioning element.

AMPERSANDlt;bodyAMPERSANDgt; AMPERSANDlt;h1AMPERSANDgt;XAMPERSANDlt;/h1AMPERSANDgt; AMPERSANDlt;h2AMPERSANDgt;XAMPERSANDlt;/h2AMPERSANDgt; AMPERSANDlt;blockquoteAMPERSANDgt;  AMPERSANDlt;h3AMPERSANDgt;XAMPERSANDlt;/h3AMPERSANDgt; AMPERSANDlt;/blockquoteAMPERSANDgt; AMPERSANDlt;p id="a"AMPERSANDgt;XAMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;h4AMPERSANDgt;Text Node AAMPERSANDlt;/h4AMPERSANDgt; AMPERSANDlt;sectionAMPERSANDgt;  AMPERSANDlt;h5AMPERSANDgt;XAMPERSANDlt;/h5AMPERSANDgt; AMPERSANDlt;/sectionAMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;Text Node BAMPERSANDlt;/pAMPERSANDgt;AMPERSANDlt;/bodyAMPERSANDgt;

3.9. Prose

3.9.1. The p element

Block-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Content model:

Significant inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

copyright, error, example, issue, note, search, warning

DOM interface:

No difference from HTMLElement.

The p element represents a paragraph.

p elements can contain a mixture of strictly inline-level content, such as text, images, hyperlinks, etc, and structured inline-level elements, such as lists, tables, and block quotes. p elements must not be empty.

AMPERSANDlt;pAMPERSANDgt;The little kitten gently seated himself on a piece ofcarpet. Later in his life, this would be referred to as the time thecat sat on the mat.AMPERSANDlt;/pAMPERSANDgt;

AMPERSANDlt;fieldsetAMPERSANDgt; AMPERSANDlt;legendAMPERSANDgt;Personal informationAMPERSANDlt;/legendAMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;   AMPERSANDlt;labelAMPERSANDgt;Name: AMPERSANDlt;input name="n"AMPERSANDgt;AMPERSANDlt;/labelAMPERSANDgt;   AMPERSANDlt;labelAMPERSANDgt;AMPERSANDlt;input name="anon" type="checkbox"AMPERSANDgt; Hide from other usersAMPERSANDlt;/labelAMPERSANDgt; AMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;AMPERSANDlt;labelAMPERSANDgt;Address: AMPERSANDlt;textarea name="a"AMPERSANDgt;AMPERSANDlt;/textareaAMPERSANDgt;AMPERSANDlt;/labelAMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;AMPERSANDlt;/fieldsetAMPERSANDgt;

AMPERSANDlt;pAMPERSANDgt;There was once an example from Femley,AMPERSANDlt;brAMPERSANDgt;Whose markup was of dubious quality.AMPERSANDlt;brAMPERSANDgt;The validator complained,AMPERSANDlt;brAMPERSANDgt;So the author was pained,AMPERSANDlt;brAMPERSANDgt;To move the error from the markup to the rhyming.AMPERSANDlt;/pAMPERSANDgt;

The p element should not be used when a more specific element is more appropriate.

AMPERSANDlt;sectionAMPERSANDgt; AMPERSANDlt;!-- ... --AMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;Last modified: 2001-04-23AMPERSANDlt;/pAMPERSANDgt; AMPERSANDlt;pAMPERSANDgt;Author: fred@example.comAMPERSANDlt;/pAMPERSANDgt;AMPERSANDlt;/sectionAMPERSANDgt;

AMPERSANDlt;sectionAMPERSANDgt; AMPERSANDlt;!-- ... --AMPERSANDgt; AMPERSANDlt;footerAMPERSANDgt;Last modified: 2001-04-23AMPERSANDlt;/footerAMPERSANDgt; AMPERSANDlt;addressAMPERSANDgt;Author: fred@example.comAMPERSANDlt;/addressAMPERSANDgt;AMPERSANDlt;/sectionAMPERSANDgt;

AMPERSANDlt;sectionAMPERSANDgt; AMPERSANDlt;!-- ... --AMPERSANDgt; AMPERSANDlt;footerAMPERSANDgt;  AMPERSANDlt;pAMPERSANDgt;Last modified: 2001-04-23AMPERSANDlt;/pAMPERSANDgt;  AMPERSANDlt;addressAMPERSANDgt;Author: fred@example.comAMPERSANDlt;/addressAMPERSANDgt; AMPERSANDlt;/footerAMPERSANDgt;AMPERSANDlt;/sectionAMPERSANDgt;

3.9.2. The hr element

Block-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Content model:

Empty.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The hr element represents a paragraph-level thematic break, e.g. a scene change in a story, or a transition to another topic within a section of a reference book.

3.9.3. The br element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

Empty.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The br element represents a line break.

br elements must be empty. Any content inside br elements must not be considered part of the surrounding text.

br elements must only be used for line breaks that are actually part of the content, as in poems or addresses.

AMPERSANDlt;pAMPERSANDgt;P. ShermanAMPERSANDlt;brAMPERSANDgt;42 Wallaby WayAMPERSANDlt;brAMPERSANDgt;SydneyAMPERSANDlt;/pAMPERSANDgt;

br elements must not be used for separating thematic groups in a paragraph.

AMPERSANDlt;pAMPERSANDgt;AMPERSANDlt;a ...AMPERSANDgt;34 comments.AMPERSANDlt;/aAMPERSANDgt;AMPERSANDlt;brAMPERSANDgt;AMPERSANDlt;a ...AMPERSANDgt;Add a comment.AMPERSANDlt;aAMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;

AMPERSANDlt;pAMPERSANDgt;Name: AMPERSANDlt;input name="name"AMPERSANDgt;AMPERSANDlt;brAMPERSANDgt;Address: AMPERSANDlt;input name="address"AMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;

AMPERSANDlt;pAMPERSANDgt;AMPERSANDlt;a ...AMPERSANDgt;34 comments.AMPERSANDlt;/aAMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;AMPERSANDlt;pAMPERSANDgt;AMPERSANDlt;a ...AMPERSANDgt;Add a comment.AMPERSANDlt;aAMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;

AMPERSANDlt;pAMPERSANDgt;Name: AMPERSANDlt;input name="name"AMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;AMPERSANDlt;pAMPERSANDgt;Address: AMPERSANDlt;input name="address"AMPERSANDgt;AMPERSANDlt;/pAMPERSANDgt;

3.9.4. The dialog element

Block-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Content model:

Zero or more pairs of dt and dd elements.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The dialog element represents a conversation.

Each part of the conversation must have an explicit talker (or speaker) given by a dt element, and a discourse (or quote) given by a dd element.

AMPERSANDlt;dialog> AMPERSANDlt;dt>Costello AMPERSANDlt;dd> Look, you gotta first baseman? AMPERSANDlt;dt> Abbott AMPERSANDlt;dd> Certainly. AMPERSANDlt;dt> Costello AMPERSANDlt;dd> Who's playing first? AMPERSANDlt;dt> Abbott AMPERSANDlt;dd> That's right. AMPERSANDlt;dt> Costello AMPERSANDlt;dd> When you pay off the first baseman every month, who gets the money? AMPERSANDlt;dt> Abbott AMPERSANDlt;dd> Every dollar of it. AMPERSANDlt;/dialog>

Text in a dt element in a dialog element is implicitly the source of the text given in the following dd element, and the contents of the dd element are implicitly a quote from that speaker. There is thus no need to include cite, q, or blockquote elements in this markup. Indeed, a q element inside a dd element in a conversation would actually imply the person talking were themselves quoting someone else. See the cite, q, and blockquote elements for other ways to cite or quote.

3.10. Preformatted text

3.10.1. The pre element

Block-level element, and structured inline-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Where structured inline-level elements are allowed.

Content model:

Strictly inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The pre element represents a block of preformatted text, in which structure is represented by typographic conventions rather than by elements.

Some examples of cases where the pre element could be used:

• Including an e-mail, with paragraphs indicated by blank lines, lists indicated by lines prefixed with a bullet, and so on.
• Including fragments of computer code, with structure indicated according to the conventions of that language.
• Displaying ASCII art.

If, ignoring text nodes consisting only of whitespace, the only child of a pre is a code element, then the pre element represents a block of computer code.

If, ignoring text nodes consisting only of whitespace, the only child of a pre is a samp element, then the pre element represents a block of computer output.

3.11. Lists

3.11.1. The ol element

Block-level element, and structured inline-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Where structured inline-level elements are allowed.

Content model:

Zero or more li elements.

Element-specific attributes:

start

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLOListElement : HTMLElement {           attribute long start;};

The ol element represents an ordered list of items (which are represented by li elements).

The start attribute, if present, must have a value that consists of an optional U+002D HYPHEN-MINUS followed by one or more digits (U+0030 to U+0039) expressing a base ten integer giving the ordinal value of the first list item.

If the start attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. The default value, used if the attribute is missing or if the value cannot be converted to a number according to the referenced algorithm, is 1.

The items of the list are the li element child nodes of the ol element, in tree order.

The first item in the list has the ordinal value given by the ol element's start attribute (unless it is further overridden by that li element's value attribute).

Each subsequent item in the list has the ordinal value given by its value attribute, if it has one, or, if it doesn't, the ordinal value of the previous item, plus one.

The start DOM attribute must reflect the value of the start content attribute.

3.11.2. The ul element

Block-level element, and structured inline-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Where structured inline-level elements are allowed.

Content model:

Zero or more li elements.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The ul element represents an unordered list of items (which are represented by li elements).

The items of the list are the li element child nodes of the ul element.

3.11.3. The li element

Contexts in which this element may be used:

Inside ol elements.

Inside ul elements.

Inside menu elements.

Content model:

When the element is a child of an ol or ul element and the grandchild of an element that is being used as an inline-level content container, or, when the element is a child of a menu element: inline-level content.

Otherwise: zero or more block-level elements, or inline-level content (but not both).

Element-specific attributes:

If the element is a child of an ol element: value

If the element is not the child of an ol element: None.

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLLIElement : HTMLElement {           attribute long value;};

The li element represents a list item. If its parent element is an ol, ul, or menu element, then the element is an item of the parent element's list, as defined for those elements. Otherwise, the list item has no defined list-related relationship to any other li element.

When the list item is the child of an ol or ul element, the content model of the item depends on the way that parent element was used. If it was used as structured inline content (i.e. if that element's parent was used as an inline-level content container), then the li element must only contain inline-level content. Otherwise, the element may be used either for inline content or block-level elements.

When the list item is the child of a menu element, the li element must contain only inline-level content.

When the list item is not the child of an ol, ul, or menu element, e.g. because it is an orphaned node not in the document, it may contain either for inline content or block-level elements.

When used as an inline-level content container, the list item represents a single paragraph.

The value attribute, if present, must have a value that consists of an optional U+002D HYPHEN-MINUS followed by one or more digits (U+0030 to U+0039) expressing a base ten integer giving the ordinal value of the first list item.

If the value attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. If the attribute's value cannot be converted to a number, it is treated as if the attribute was absent. The attribute has no default value.

The value attribute is processed relative to the element's parent ol element, if there is one. If there is not, the attribute has no effect.

The value DOM attribute must reflect the value of the value content attribute.

3.11.4. The dl element

Block-level element, and structured inline-level element.

Contexts in which this element may be used:

Where block-level elements are expected.

Where structured inline-level elements are allowed.

Content model:

Zero or more groups each consisting of one or more dt elements followed by one or mode dd elements.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The dl element introduces an unordered association list consisting of zero or more name-value groups (a description list). Each group must consist of one or more names (dt elements) followed by one or more values (dd elements).

Name-value groups may be terms and definitions, metadata topics and values, or any other groups of name-value data.

AMPERSANDlt;dlAMPERSANDgt; AMPERSANDlt;dtAMPERSANDgt; Authors AMPERSANDlt;ddAMPERSANDgt; John AMPERSANDlt;ddAMPERSANDgt; Luke AMPERSANDlt;dtAMPERSANDgt; Editor AMPERSANDlt;ddAMPERSANDgt; FrankAMPERSANDlt;/dlAMPERSANDgt;

AMPERSANDlt;dlAMPERSANDgt; AMPERSANDlt;dt lang="en-US"AMPERSANDgt; AMPERSANDlt;dfn>colorAMPERSANDlt;/dfn> AMPERSANDlt;/dtAMPERSANDgt; AMPERSANDlt;dt lang="en-GB"AMPERSANDgt; AMPERSANDlt;dfn>colourAMPERSANDlt;/dfn> AMPERSANDlt;/dtAMPERSANDgt; AMPERSANDlt;ddAMPERSANDgt; A sensation which (in humans) derives from the ability of the fine structure of the eye to distinguish three differently filtered analyses of a view. AMPERSANDlt;/ddAMPERSANDgt;AMPERSANDlt;/dlAMPERSANDgt;

AMPERSANDlt;dlAMPERSANDgt; AMPERSANDlt;dtAMPERSANDgt; Last modified time AMPERSANDlt;/dtAMPERSANDgt; AMPERSANDlt;ddAMPERSANDgt; 2004-12-23T23:33Z AMPERSANDlt;/ddAMPERSANDgt; AMPERSANDlt;dtAMPERSANDgt; Recommended update interval AMPERSANDlt;/dtAMPERSANDgt; AMPERSANDlt;ddAMPERSANDgt; 60s AMPERSANDlt;/ddAMPERSANDgt; AMPERSANDlt;dtAMPERSANDgt; Authors AMPERSANDlt;/dtAMPERSANDgt; AMPERSANDlt;dtAMPERSANDgt; Editors AMPERSANDlt;/dtAMPERSANDgt; AMPERSANDlt;ddAMPERSANDgt; Robert Rothman AMPERSANDlt;/ddAMPERSANDgt; AMPERSANDlt;ddAMPERSANDgt; Daniel Jackson AMPERSANDlt;/ddAMPERSANDgt;AMPERSANDlt;/dlAMPERSANDgt;

If a dl element is empty, it contains no groups.

If a dl element contains non-whitespace text nodes, or elements other than dt and dd, then those elements or text nodes do not form part of any groups in that dl, and the document is non-conforming.

If a dl element contains only dt elements, then it consists of one group with names but no values, and the document is non-conforming.

If a dl element contains only dd elements, then it consists of one group with values but no names, and the document is non-conforming.

The dl element is inappropriate for marking up dialogue, since dialogue is ordered (each speaker/line pair comes after the next). For an example of how to mark up dialogue, see the dialog element.

3.11.5. The dt element

Contexts in which this element may be used:

Before dd or dt elements inside dl elements.

Before a dd element inside a dialog element.

Content model:

Strictly inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The dt element represents the term, or name, part of a term-description group in a description list (dl element), and the talker, or speaker, part of a talker-discourse pair in a conversation (dialog element).

The dt element itself, when used in a dl element, does not indicate that its contents are a term being defined, but this can be indicated using the dfn element.

3.11.6. The dd element

Contexts in which this element may be used:

After dt or dd elements inside dl elements.

After a dt element inside a dialog element.

Content model:

When the element is a child of a dl element and the grandchild of an element that is being used as an inline-level content container: inline-level content.

Otherwise: zero or more block-level elements, or inline-level content (but not both).

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The dd element represents the description, definition, or value, part of a term-description group in a description list (dl element), and the discourse, or quote, part in a conversation (dialog element).

The content model of a dd element depends on the way its parent element is being used. If the parent element is a dl element that is being used as structured inline content (i.e. if the dl element's parent element is being used as an inline-level content container), then the dd element must only contain inline-level content.

Otherwise, the element may be used either for inline content or block-level elements.

3.12. Phrase elements

3.12.1. The a element

Interactive, strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed, if there are no ancestor interactive elements.

Content model:

When used in an element whose content model is only strictly inline-level content: only significant strictly inline-level content, but there must be no interactive descendants.

Otherwise: any significant inline-level content, but there must be no interactive descendants.

Element-specific attributes:

href

rel

media

hreflang

type

ping

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLAnchorElement : HTMLElement {           attribute DOMString href;           attribute DOMString rel;           attribute DOMString media;           attribute DOMString hreflang;           attribute DOMString type;           attribute DOMString ping;};

The Command interface must also be implemented by this element.

If the a element has an href attribute, then it represents a hyperlink.

If the a element has no href attribute, then the element is a placeholder for where a link might otherwise have been placed, if it had been relevant.

AMPERSANDlt;nav> AMPERSANDlt;ul>  AMPERSANDlt;li> AMPERSANDlt;a href="/">HomeAMPERSANDlt;/a> AMPERSANDlt;/li>  AMPERSANDlt;li> AMPERSANDlt;a href="/news">NewsAMPERSANDlt;/a> AMPERSANDlt;/li>  AMPERSANDlt;li> AMPERSANDlt;a>ExamplesAMPERSANDlt;/a> AMPERSANDlt;/li>  AMPERSANDlt;li> AMPERSANDlt;a href="/legal">LegalAMPERSANDlt;/a> AMPERSANDlt;/li> AMPERSANDlt;/ul>AMPERSANDlt;/nav>

Interactive user agents should allow users to follow hyperlinks created using the a element. The href and ping attributes decide how the link is followed. The rel, media, hreflang, and type attributes may be used to indicate to the user the likely nature of the target resource before the user follows the link.

default action of clicking a link is to check if target was an image with ismap; if so, do server-side image map processing, otherwise, fire DOMActivate on the link.

The a element must not be empty.

The DOM attributes href, rel, media, hreflang, type, and ping each must reflect the respective content attributes of the same name.

3.12.2. The q element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.

Otherwise: any inline-level content.

Element-specific attributes:

cite

Predefined classes that apply to this element:

None.

DOM interface:

The q element uses the HTMLQuoteElement interface.

The q element represents a part of a paragraph quoted from another source.

Content inside a q element must be quoted from another source, whose URI, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a URI (or IRI). User agents should allow users to follow such citation links.

If a q element is contained (directly or indirectly) in a paragraph that contains a single cite element and has no other q element descendants, then, the citation given by that cite element gives the source of the quotation contained in the q element.

3.12.3. The cite element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

Strictly inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The cite element represents a citation: the source, or reference, for a quote or statement made in the document.

A citation is not a quote (for which the q element is appropriate).

AMPERSANDlt;p>AMPERSANDlt;cite>This is wrong!AMPERSANDlt;/cite>, said Ian.AMPERSANDlt;/p>

AMPERSANDlt;p>AMPERSANDlt;q>This is correct!AMPERSANDlt;/q>, said AMPERSANDlt;cite>IanAMPERSANDlt;/cite>.AMPERSANDlt;/p>

AMPERSANDlt;p>My favourite book is AMPERSANDlt;cite>The Reality DysfunctionAMPERSANDlt;/cite>by AMPERSANDlt;cite>Peter F. HamiltonAMPERSANDlt;/cite>.AMPERSANDlt;/p>

AMPERSANDlt;p>According to AMPERSANDlt;cite>the Wikipedia article onHTMLAMPERSANDlt;/cite>, HTML is defined in formal specifications that weredeveloped and published throughout the 1990s.AMPERSANDlt;/p>

The cite element can apply to blockquote and q elements in certain cases described in the definitions of those elements.

3.12.4. The em element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.

Otherwise: any inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The em element represents stress emphasis of its contents.

The level of emphasis that a particlar piece of content has is given by its number of ancestor em elements.

The placement of emphasis changes the meaning of the sentence. The element thus forms an integral part of the content. The precise way in which emphasis is used in this way depends on the language.

AMPERSANDlt;p>Cats are cute animals.AMPERSANDlt;/p>

AMPERSANDlt;p>AMPERSANDlt;em>CatsAMPERSANDlt;/em> are cute animals.AMPERSANDlt;/p>

AMPERSANDlt;p>Cats AMPERSANDlt;em>areAMPERSANDlt;/em> cute animals.AMPERSANDlt;/p>

AMPERSANDlt;p>Cats are AMPERSANDlt;em>cuteAMPERSANDlt;/em> animals.AMPERSANDlt;/p>

AMPERSANDlt;p>Cats are cute AMPERSANDlt;em>animalsAMPERSANDlt;/em>.AMPERSANDlt;/p>

AMPERSANDlt;p>AMPERSANDlt;em>Cats are cute animals!AMPERSANDlt;/em>AMPERSANDlt;/p>

AMPERSANDlt;p>AMPERSANDlt;em>Cats are AMPERSANDlt;em>cuteAMPERSANDlt;/em> animals!AMPERSANDlt;/em>AMPERSANDlt;/p>

3.12.5. The strong element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.

Otherwise: any inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

error, warning

DOM interface:

No difference from HTMLElement.

The strong element represents strong importance for its contents.

The relative level of importance of a piece of content is given by its number of ancestor strong elements; each strong element increases the importance of its contents.

Changing the importance of a piece of text with the strong element does not change the meaning of the sentence.

AMPERSANDlt;p>AMPERSANDlt;strong>Warning.AMPERSANDlt;/strong> This dungeon is dangerous.AMPERSANDlt;strong>Avoid the ducks.AMPERSANDlt;/strong> Take any gold you find.AMPERSANDlt;strong>AMPERSANDlt;strong>Do not take any of the diamondsAMPERSANDlt;/strong>,they are explosive and AMPERSANDlt;strong>will destroy anything withinten meters.AMPERSANDlt;/strong>AMPERSANDlt;/strong> You have been warned.AMPERSANDlt;/p>

3.12.6. The small element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.

Otherwise: any inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The small element represents small print (part of a document often describing legal restrictions, such as copyrights or other disadvantages), or other side comments.

The small element does not "de-emphasise" or lower the importance of text emphasised by the em element or marked as important with the strong element.

AMPERSANDlt;footer> AMPERSANDlt;address>  For more details, contact  AMPERSANDlt;a href="mailto:js@example.com">John SmithAMPERSANDlt;/a>. AMPERSANDlt;/address> AMPERSANDlt;p>AMPERSANDlt;small>AMPERSANDcopy; copyright 2038 Example Corp.AMPERSANDlt;/small>AMPERSANDlt;/p>AMPERSANDlt;/footer>

AMPERSANDlt;p>Example Corp today announced record profits for thesecond quarter AMPERSANDlt;small>(Full Disclosure: Foo News is a subsidiary ofExample Corp)AMPERSANDlt;/small>, leading to speculation about a third quartermerger with Demo Group.AMPERSANDlt;/p>

AMPERSANDlt;p>AMPERSANDlt;strong>AMPERSANDlt;small>Continued use of this service will result in a kiss.AMPERSANDlt;/small>AMPERSANDlt;/strong>AMPERSANDlt;/p>

3.12.7. The m element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.

Otherwise: any inline-level content.

Element-specific attributes:

None.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The m element represents a run of text marked or highlighted.

AMPERSANDlt;p>The highlighted part below is where the error lies:AMPERSANDlt;/p>AMPERSANDlt;pre>AMPERSANDlt;code>var i: Integer;begin   i := AMPERSANDlt;m>1.1AMPERSANDlt;/m>;end.AMPERSANDlt;/code>AMPERSANDlt;/pre>

AMPERSANDlt;p>I also have some AMPERSANDlt;m>kittenAMPERSANDlt;/m>s who are visiting methese days. They're really cute. I think they like my garden!AMPERSANDlt;/p>

3.12.8. The dfn element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed, if there are no ancestor dfn elements.

Content model:

Strictly inline-level content, but there must be no descendant dfn elements.

Element-specific attributes:

None, but the title attribute has special semantics on this element.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The dfn element represents the defining instance of a term. The paragraph, description list group, or section that contains the dfn element contains the definition for the term given by the contents of the dfn element.

dfn elements must not be nested.

Defining term: If the dfn element has a title attribute, then the exact value of that attribute is the term being defined. Otherwise, if it contains exactly one element child node and no child text nodes, and that child element is an abbr element with a title attribute, then the exact value of that attribute is the term being defined. Otherwise, it is the exact textContent of the dfn element that gives the term being defined.

If the title attribute of the dfn element is present, then it must only contain the term being defined.

There must only be one dfn element per document for each term defined (i.e. there must not be any duplicate terms).

The title attribute of ancestor elements does not affect dfn elements.

The dfn element enables automatic cross-references. Specifically, any span, abbr, code, var, samp, or i element that has a non-empty title attribute whose value exactly equals the term of a dfn element in the same document, or which has no title attribute but whose textContent exactly equals the term of a dfn element in the document, and that has no interactive elements or dfn elements either as ancestors or descendants, and has no other elements as ancestors that are themselves matching these conditions, should be presented in such a way that the user can jump from the element to the first dfn element giving the defining instance of that term.

AMPERSANDlt;p>The AMPERSANDlt;dfn>AMPERSANDlt;abbr title="Garage Door Opener">GDOAMPERSANDlt;/abbr>AMPERSANDlt;/dfn>is a device that allows off-world teams to open the iris.AMPERSANDlt;/p>AMPERSANDlt;!-- ... later in the document: -->AMPERSANDlt;p>Teal'c activated his AMPERSANDlt;abbr title="Garage Door Opener">GDOAMPERSANDlt;/abbr>and so Hammond ordered the iris to be opened.AMPERSANDlt;/p>

3.12.9. The abbr element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

Strictly inline-level content.

Element-specific attributes:

None, but the title attribute has special semantics on this element.

Predefined classes that apply to this element:

None.

DOM interface:

No difference from HTMLElement.

The abbr element represents an abbreviation or acronym. The title attribute should be used to provide an expansion of the abbreviation. If present, the attribute must only contain an expansion of the abbreviation.

AMPERSANDlt;p>The AMPERSANDlt;abbr title="Web Hypertext Application TechnologyWorking Group">WHATWGAMPERSANDlt;/abbr> is a loose unofficial collaboration ofWeb browser manufacturers and interested parties who wish to developnew technologies designed to allow authors to write and deployApplications over the World Wide Web.AMPERSANDlt;/p>

The title attribute may be omitted if there is a dfn element in the document whose defining term is the abbreviation (the textContent of the abbr element).

AMPERSANDlt;p>The AMPERSANDlt;dfn>AMPERSANDlt;abbr>ZatAMPERSANDlt;/abbr>AMPERSANDlt;/dfn>, short for Zat'ni'catel, is a weapon.AMPERSANDlt;/p>AMPERSANDlt;p>Jack used a AMPERSANDlt;abbr>ZatAMPERSANDlt;/abbr> to make the boxes of evidence disappear.AMPERSANDlt;/p>

3.12.10. The time element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

Strictly inline-level content.

Element-specific attributes:

datetime

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLTimeElement : HTMLElement {           attribute DOMString datetime;  readonly attribute DOMTimeStamp date;  readonly attribute DOMTimeStamp time;  readonly attribute DOMTimeStamp timezone;};

The time element represents a date and/or a time.

The datetime attribute, if present, must contain a date or time string that identifies the date or time being specified.

If the datetime attribute is not present, then the date or time must be specified in the content of the element, such that parsing the element's textContent according to the rules for parsing date or time strings in content successfully extracts a date or time.

The datetime DOM attribute must reflect the datetime content attribute.

User agents, to obtain the date, time, and timezone represented by a time element, must follow the following steps:

1. If the datetime attribute is present, then parse it according to the rules for parsing date or time strings in content, and let the result be result.
2. Otherwise, parse the element's textContent according to the rules for parsing date or time strings in content, and let the result be result.
3. If result is empty (because the parsing failed), then the date is unknown, the time is unknown, and the timezone is unknown.
4. Otherwise: if result contains a date, then that is the date; if result contains a time, then that is the time; and if result contains a timezone, then the timezone is the element's timezone. (A timezone can only be present if both a date and a time are also present.)

The date DOM attribute must return null if the date is unknown, and otherwise must return the time corresponding to midnight UTC (i.e. the first second) of the given date.

The time DOM attribute must return null if the time is unknown, and otherwise must return the time corresponding to the given time of 1970-01-01, with the timezone UTC.

The timezone DOM attribute must return null if the timezone is unknown, and otherwise must return the time corresponding to 1970-01-01 00:00 UTC in the given timezone, with the timezone set to UTC (i.e. the time corresponding to 1970-01-01 at 00:00 UTC plus the offset corresponding to the timezone).

AMPERSANDlt;p>Our first date was AMPERSANDlt;time datetime="2006-09-23">a saturdayAMPERSANDlt;/time>.AMPERSANDlt;/p>

AMPERSANDlt;p>We stopped talking at AMPERSANDlt;time datetime="2006-09-24 05:00 -7">5am the next morningAMPERSANDlt;/time>.AMPERSANDlt;/p>

AMPERSANDlt;p>Many people get up at AMPERSANDlt;time>08:00AMPERSANDlt;/time>.AMPERSANDlt;/p>

These APIs may be suboptimal. Comments on making them more useful to JS authors are welcome. The primary use cases for these elements are for marking up publication dates e.g. in blog entries, and for marking event dates in hCalendar markup. Thus the DOM APIs are likely to be used as ways to generate interactive calendar widgets or some such.

3.12.11. The meter element

Strictly inline-level content.

Contexts in which this element may be used:

Where strictly inline-level content is allowed.

Content model:

Strictly inline-level content.

Element-specific attributes:

value

min

low

high

max

optimum

Predefined classes that apply to this element:

None.

DOM interface:

interface HTMLMeterElement : HTMLElement {           attribute long value;           attribute long min;           attribute long max;           attribute long low;           attribute long high;           attribute long optimum;};

The meter element represents a scalar measurement within a known range, or a fractional value; for example disk usage, the relevance of a query result, or the fraction of a voting population to have selected a particular candidate.

This is also known as a gauge.

The meter element should not be used to indicate progress (as in a progress bar). For that role, HTML provides a separate progress element.

There are six attributes that determine the semantics of the gauge represented by the element.

The min attribute specifies the lower bound of the range, and the max attribute specifies the upper bound. The value attribute specifies the value to have the gauge indicate as the "measured" value.

The other three attributes can be used to segment the gauge's range into "low", "medium", and "high" parts, and to indicate which part of the gauge is the "optimum" part. The low attribute specifies the range that is considered to be the "low" part, and the high attribute specifies the range that is considered to be the "high" part. The optimum attribute gives the position that is "optimum"; if that is higher than the "high" value then this indicates that the higher the value, the better; if it's lower than the "low" mark then it indicates that lower values are better, and naturally if it is in between then it indicates that neither high nor low values are good.

Authoring requirements: The recommended way of giving the value is to include it as contents of the element, either as two numbers (the higher number represents the maximum, the other number the current value), or as a percentage or similar (using one of the characters such as "%"), or as a fraction.

The value, min, low, high, max, and optimum attributes are all optional. When present, they must have values that are valid floating point numbers.

AMPERSANDlt;meter>75%AMPERSANDlt;/meter>AMPERSANDlt;meter>750AMPERSAND#x2030;AMPERSANDlt;/meter>AMPERSANDlt;meter>3/4AMPERSANDlt;/meter>AMPERSANDlt;meter>6 blocks used (out of 8 total)AMPERSANDlt;/meter>AMPERSANDlt;meter>max: 100; current: 75AMPERSANDlt;/meter>AMPERSANDlt;meter>AMPERSANDlt;object data="graph75.png">0.75AMPERSANDlt;/object>AMPERSANDlt;/meter>AMPERSANDlt;meter min="0" max="100" value="75">AMPERSANDlt;/meter>

User agent requirements: User agents must parse the min, max, value, low, high, and optimum attributes using the rules for parsing floating point number values.

If the value attribute has been omitted, the user agent must also process the textContent of the element according to the steps for finding one or two numbers of a ratio in a string. These steps will return nothing, one number, one number with a denominator punctuation character, or two numbers.

User agents must then use all these numbers to obtain values for six points on the gauge, as follows. (The order in which these are evaluated is important, as some of the values refer to earlier ones.)

The minimum value

If the min attribute is specified and a value could be parsed out of it, then the minimum value is that value. Otherwise, the minimum value is zero.

The maximum value

If the max attribute is specified and a value could be parsed out of it, the maximum value is that value.

Otherwise, if the max attribute is specified but no value could be parsed out of it, or if it was not specified, but either or both of the min or value attributes were specified, then the maximum value is 1.

Otherwise, none of the max, min, and value attributes were specified. If the result of processing the textContent of the element was either nothing or just one number with no denominator punctuation character, then the maximum value is 1; if the result was one number but it had an associated denominator punctuation character, then the maximum value is the value associated with that denominator punctuation character; and finally, if there were two numbers parsed out of the textContent, then the maximum is the higher of those two numbers.

If the above machinations result in a maximum value less than the minimum value, then the maximum value is actually the same as the minimum value.

The actual value

If the value attribute is specified and a value could be parsed out of it, then that value is the actual value.

If the value attribute is not specified but the max attribute is specified and the result of processing the textContent of the element was one number with no associated denominator punctuation character, then that number is the actual value.

If neither of the value and max attributes are specified, then, if the result of processing the textContent of the element was one number (with or without an associated denominator punctuation character), then that is the actual value, and if the result of processing the textContent of the element was two numbers, then the actual value is the lower of the two numbers found.

Otherwise, if none of the above apply, the actual value is zero.

If the above procedure results in an actual value less than the minimum value, then the actual value is actually the same as the minimum value.

If, on the other hand, the result is an actual value greater than the maximum value, then the actual value is the maximum value.

The low boundary

If the low attribute is specified and a value could be parsed out of it, then the low boundary is that value. Otherwise, the low boundary is the same as the minimum value.

If the above results in a low boundary that is less than the minimum value, the low boundary is the minimum value.

The high boundary

If the high attribute is specified and a value could be parsed out of it, then the high boundary is that value. Otherwise, the high boundary is the same as the maximum value.

If the above results in a high boundary that is higher than the maximum value, the high boundary is the maximum value.

The optimum point

If the optimum attribute is specified and a value could be parsed out of it, then the optimum point is that value. Otherwise, the optimum point is the midpoint between the minimum value and the maximum value.

If the optimum point is then less than the minimum value, then the optimum point is actually the same as the minimum value. Similarly, if the optimum point is greater than the maximum value, then it is actually the maximum value instead.