HTML 5.1

None.

As the root element of a document.

Wherever a subdocument fragment is allowed in a compound document.

A head element followed by a body element.

An html element’s start tag can be omitted if the first thing inside the html element is not a comment.

An html element’s end tag can be omitted if the html element is not immediately followed by a comment.

manifest — Application cache manifest

Allowed ARIA role attribute values:

None

interface HTMLHtmlElement : HTMLElement {};

The html element represents the root of an HTML document.

Authors are encouraged to specify a lang attribute on the root html element, giving the document’s language. This aids speech synthesis tools to determine what pronunciations to use, translation tools to determine what rules to use, and so forth.

The manifest attribute gives the address of the document’s application cache manifest, if there is one. If the attribute is present, the attribute’s value must be a valid non-empty URL potentially surrounded by spaces.

The manifest attribute only has an effect during the early stages of document load. Changing the attribute dynamically thus has no effect (and thus, no DOM API is provided for this attribute).

For the purposes of application cache selection, later base elements cannot affect the resolving of relative URLs in manifest attributes, as the attributes are processed before those elements are seen.

The window.applicationCache IDL attribute provides scripted access to the offline application cache mechanism.

The html element in the following example declares that the document’s language is English.

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Swapping Songs</title>
  </head>
  <body>
    <h1>Swapping Songs</h1>
    <p>Tonight I swapped some of the songs I wrote with some friends, who
    gave me some of the songs they wrote. I love sharing my music.</p>
  </body>
</html>

4.2. Document metadata

4.2.1. The `head` element

None.

As the first element in an html element.

If the document is an iframe srcdoc document or if title information is available from a higher-level protocol: Zero or more elements of metadata content, of which no more than one is a title element and no more than one is a base element.

Otherwise: One or more elements of metadata content, of which exactly one is a title element and no more than one is a base element.

A head element’s start tag may be omitted if the element is empty, or if the first thing inside the head element is an element.

A head element’s end tag may be omitted if the head element is not immediately followed by a space character or a comment.

Allowed ARIA role attribute values:

None

interface HTMLHeadElement : HTMLElement {};

The head element represents a collection of metadata for the Document.

The collection of metadata in a head element can be large or small. Here is an example of a very short one:

<!doctype html>
<html>
  <head>
    <title>A document with a short head</title>
  </head>
  <body>
    ...

Here is an example of a longer one:

<!DOCTYPE HTML>
  <HTML>
  <HEAD>
    <META CHARSET="UTF-8">
    <BASE HREF="http://www.example.com/">
    <TITLE>An application with a long head</TITLE>
    <LINK REL="STYLESHEET" HREF="default.css">
    <LINK REL="STYLESHEET ALTERNATE" HREF="big.css" TITLE="Big Text">
    <SCRIPT SRC="support.js"></SCRIPT>
    <META NAME="APPLICATION-NAME" CONTENT="Long headed application">
  </HEAD>
  <BODY>
    ...

The title element is a required child in most situations, but when a higher-level protocol provides title information, e.g., in the Subject line of an e-mail when HTML is used as an e-mail authoring format, the title element can be omitted.

4.2.2. The `title` element

Metadata content.

In a head element containing no other title elements.

Text that is not inter-element whitespace.

Neither tag is omissible.

Allowed ARIA role attribute values:

None

interface HTMLTitleElement : HTMLElement {
  attribute DOMString text;
};

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 heading, since the first heading does not have to stand alone when taken out of context.

There must be no more than one title element per document.

If it’s reasonable for the Document to have no title, then the title element is probably not required. See the head element’s content model for a description of when the element is required.

title . text [ = value ]: Returns the contents of the element, ignoring child nodes that aren’t Text nodes.
Can be set, to replace the element’s children with the given value.

The IDL attribute text must return a concatenation of the contents of all the Text nodes that are children of the title element (ignoring any other nodes such as comments or elements), in tree order. On setting, it must act the same way as the textContent IDL attribute.

Here are some examples of appropriate titles, contrasted with the top-level headings that might be used on those same pages.

<title>Introduction to The Mating Rituals of Bees</title>
...
<h1>Introduction</h1>
<p>This companion guide to the highly successful
<cite>Introduction to Medieval Bee-Keeping</cite> book is...

The next page might be a part of the same site. Note how the title describes the subject matter unambiguously, while the first heading assumes the reader knows what the context is and therefore won’t wonder if the dances are Salsa or Waltz:

<title>Dances used during bee mating rituals</title>
...
<h2>The Dances</h2>

The string to use as the document’s title is given by the document.title IDL attribute.

User agents should use the document’s title when referring to the document in their user interface. When the contents of a title element are used in this way, the directionality of that title element should be used to set the directionality of the document’s title in the user interface.

4.2.3. The `base` element

Metadata content.

In a head element containing no other base elements.

Nothing.

No end tag.

href — Document base URL

target — Default browsing context for hyperlink navigation and §4.10.22 Form submission

Allowed ARIA role attribute values:

None

Global aria-* attributes.

interface HTMLBaseElement : HTMLElement {
  attribute DOMString href;
  attribute DOMString target;
};

The base element allows authors to specify the document base URL for the purposes of resolving relative URLs, and the name of the default browsing context for the purposes of following hyperlinks. The element does not represent any content beyond this information.

There must be no more than one base element per document.

A base element must have either an href attribute, a target attribute, or both.

The href content attribute, if specified, must contain a valid URL potentially surrounded by spaces.

A base element, if it has an href attribute, must come before any other elements in the tree that have attributes defined as taking URLs, except the html element (its manifest attribute isn’t affected by xml:base attributes or base elements).

If there are multiple base elements with href attributes, all but the first are ignored.

The target attribute, if specified, must contain a valid browsing context name or keyword, which specifies which browsing context is to be used as the default when hyperlinks and forms in the Document cause navigation.

A base element, if it has a target attribute, must come before any elements in the tree that represent hyperlinks.

If there are multiple base elements with target attributes, all but the first are ignored.

A base element that is the first base element with an href content attribute in a particular Document has a frozen base URL. The frozen base URL must be immediately set whenever any of the following situations occur:

The base element becomes the first base element in tree order with an href content attribute in its Document.
The base element is the first base element in tree order with an href content attribute in its Document, and its href content attribute is changed.

To set the frozen base URL, resolve the value of the element’s href content attribute relative to the Document's fallback base URL; if this is successful, set the frozen base URL to the resulting absolute URL, otherwise, set the frozen base URL to the fallback base URL.

The href IDL attribute, on getting, must return the result of running the following algorithm:

If the base element has no href content attribute, then return the document base URL and abort these steps.
Let fallback base url be the Document's fallback base URL.
Let url be the value of the href attribute of the base element.
Resolve url relative to fallback base url (thus, the base’s href attribute isn’t affected by other base elements).
If the previous step was successful, return the resulting absolute URL and abort these steps.
Otherwise, return the empty string.

The href IDL attribute, on setting, must set the href content attribute to the given new value.

The target IDL attribute must reflect the content attribute of the same name.

In this example, a base element is used to set the document base URL:

<!DOCTYPE html>
<html>
  <head>
    <title>This is an example for the &lt;base&gt; element</title>
    <base href="http://www.example.com/news/index.html">
  </head>
  <body>
    <p>Visit the <a href="archives.html">archives</a>.</p>
  </body>
</html>

The link in the above example would be a link to "http://www.example.com/news/archives.html".

4.2.4. The `link` element

Metadata content.

If the itemprop attribute is present: flow content.

If the itemprop attribute is present: phrasing content.

Where metadata content is expected.

In a noscript element that is a child of a head element.

If the itemprop attribute is present: where phrasing content is expected.

Nothing.

No end tag.

href — Address of the hyperlink

crossorigin — How the element handles crossorigin requests

rel — Relationship between the document containing the hyperlink and the destination resource

media — Applicable media

hreflang — Language of the linked resource

type — Hint for the type of the referenced resource

sizes — Sizes of the icons (for rel="icon")

Also, the title attribute has special semantics on this element: Title of the link; alternative style sheet set name.

Allowed ARIA role attribute values:

link (default - do not set).

Any aria-* attributes applicable to the allowed roles.

For role value

interface HTMLLinkElement : HTMLElement {
  attribute DOMString href;
  attribute DOMString? crossOrigin;
  attribute DOMString rel;

  attribute DOMString rev;
  readonly attribute DOMTokenList relList;
  attribute DOMString media;
  attribute DOMString hreflang;
  attribute DOMString type;
  [PutForwards=value] readonly attribute DOMTokenList sizes;
};
HTMLLinkElement implements LinkStyle;

The link element allows authors to link their document to other resources.

The destination of the link(s) is given by the href attribute, which must be present and must contain a valid non-empty URL potentially surrounded by spaces. If the href attribute is absent, then the element does not define a link.

A link element must have either a rel attribute or an itemprop attribute, but not both.

If the rel attribute is used, the element is restricted to the head element. When used with the itemprop attribute, the element can be used both in the head element and in the body of the page, subject to the constraints of the microdata model.

The types of link indicated (the relationships) are given by the value of the rel attribute, which, if present, must have a value that is a set of space-separated tokens. The allowed keywords and their meanings are defined in a later section. If the rel attribute is absent, has no keywords, or if none of the keywords used are allowed according to the definitions in this specification, then the element does not create any links.

Two categories of links can be created using the link element: Links to external resources and hyperlinks. The §4.8.6 Link types section defines whether a particular link type is an external resource or a hyperlink. One link element can create multiple links (of which some might be external resource links and some might be hyperlinks); exactly which and how many links are created depends on the keywords given in the rel attribute. User agents must process the links on a per-link basis, not a per-element basis.

Each link created for a link element is handled separately. For instance, if there are two link elements with rel="stylesheet", they each count as a separate external resource, and each is affected by its own attributes independently. Similarly, if a single link element has a rel attribute with the value next stylesheet, it creates both a hyperlink (for the next keyword) and an external resource link (for the stylesheet keyword), and they are affected by other attributes (such as media or title) differently.

For example, the following link element creates two hyperlinks (to the same page):

<link rel="author license" href="/about">

The two links created by this element are one whose semantic is that the target page has information about the current page’s author, and one whose semantic is that the target page has information regarding the license under which the current page is provided.

The crossorigin attribute is a CORS settings attribute. It is intended for use with external resource links.

The exact behavior 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 (modulo cross-origin restrictions) even if the resource is not applied. To obtain the resource, the user agent must run the following steps:

If the href attribute’s value is the empty string, then abort these steps.
Resolve the URL given by the href attribute, relative to the element.
If the previous step fails, then abort these steps.
Let corsAttributeState be the current state of the element’s crossorigin content attribute.
Let request be the result of creating a potential-CORS request given the URL and corsAttributeState.
Set request’s client to the link element’s node document’s Window object’s environment settings object.
Fetch request.

User agents may opt to only try to obtain such resources when they are needed, instead of pro-actively fetching all the external resources that are not applied.

The semantics of the protocol used (e.g., HTTP) must be followed when fetching external resources. (For example, redirects will be followed and 404 responses will cause the external resource to not be applied.)

Once the attempts to obtain the resource and its critical subresources are complete, the user agent must, if the loads were successful, queue a task to fire a simple event named load at the link element, or, if the resource or one of its critical subresources failed to completely load for any reason (e.g., DNS error, HTTP 404 response, a connection being prematurely closed, unsupported Content-Type), queue a task to fire a simple event named error at the link element. Non-network errors in processing the resource or its subresources (e.g., CSS parse errors, PNG decoding errors) are not failures for the purposes of this paragraph.

The task source for these tasks is the DOM manipulation task source.

The element must delay the load event of the element’s node document until all the attempts to obtain the resource and its critical subresources are complete. (Resources that the user agent has not yet attempted to obtain, e.g., because it is waiting for the resource to be needed, do not delay the load event.)

Interactive user agents may 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 could 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 address 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 could also include other information, such as the type of the resource (as given by the type attribute).

Hyperlinks created with the link element and its rel attribute apply to the whole page. This contrasts with the rel attribute of a and area elements, which indicates the type of a link whose context is given by the link’s location within the document.

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

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 apply the external resource when the media attribute’s value matches the environment and the other relevant conditions apply, and must not apply it otherwise.

The external resource might have further restrictions defined within that limit its applicability. For example, a CSS style sheet might have some @media blocks. This specification does not override such further restrictions or requirements.

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 the a element.

The type attribute gives the MIME type of the linked resource. It is purely advisory. The value must be a valid mime type.

For external resource links, the type attribute is used as a hint to user agents so that they can avoid fetching resources they do not support. If the attribute is present, then the user agent must assume that the resource is of the given type (even if that is not a valid mime type, e.g., the empty string). If the attribute is omitted, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type. If the user agent does not support the given MIME type for the given link relationship, then the user agent should not obtain the resource; if the user agent does support the given MIME type for the given link relationship, then the user agent should obtain the resource at the appropriate time as specified for the external resource link’s particular type. If the attribute is omitted, and the external resource link type does not have a default type defined, but the user agent would obtain the resource if the type was known and supported, then the user agent should obtain the resource under the assumption that it will be supported.

User agents must not consider the type attribute authoritative — upon fetching the resource, user agents must not use the type attribute to determine its actual type. Only the actual type (as defined in the next paragraph) is used to determine whether to apply the resource, not the aforementioned assumed type.

If the external resource link type defines rules for processing the resource’s Content-Type metadata, then those rules apply. Otherwise, if the resource is expected to be an image, user agents may apply the image sniffing rules, with the official type being the type determined from the resource’s Content-Type metadata, and use the resulting sniffed type of the resource as if it was the actual type. Otherwise, if neither of these conditions apply or if the user agent opts not to apply the image sniffing rules, then the user agent must use the resource’s Content-Type metadata to determine the type of the resource. If there is no type metadata, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type.

The stylesheet link type defines rules for processing the resource’s Content-Type metadata.

Once the user agent has established the type of the resource, the user agent must apply the resource if it is of a supported type and the other relevant conditions apply, and must ignore the resource otherwise.

If a document contains style sheet links labeled as follows:

<link rel="stylesheet" href="A" type="text/plain">
<link rel="stylesheet" href="B" type="text/css">
<link rel="stylesheet" href="C">

...then a compliant user agent that supported only CSS style sheets would fetch the B and C files, and skip the A file (since text/plain is not the MIME type for CSS style sheets).

For files B and C, it would then check the actual types returned by the server. For those that are sent as text/css, it would apply the styles, but for those labeled as text/plain, or any other type, it would not.

If one of the two files was returned without a Content-Type metadata, or with a syntactically incorrect type like Content-Type: "null", then the default type for stylesheet links would kick in. Since that default type is text/css, the style sheet would nonetheless be applied.

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 alternative 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.

The sizes attribute is used with the icon link type. The attribute must not be specified on link elements that do not have a rel attribute that specifies the icon keyword.

The activation behavior of link elements that create hyperlinks is to run the following steps:

If the link element’s node document is not fully active, then abort these steps.
Follow the hyperlink created by thelink element.

HTTP Link: headers, if supported, must be assumed to come before any links in the document, in the order that they were given in the HTTP message. These headers are to be processed according to the rules given in the relevant specifications. [HTTP] [RFC5988]

Registration of relation types in HTTP Link: headers is distinct from HTML link types, and thus their semantics can be different from same-named HTML types.

The IDL attributes link/href, rel, rev, media, hreflang, type, and sizes each must reflect the respective content attributes of the same name.

The crossOrigin IDL attribute must reflect the crossorigin content attribute.

The IDL attribute relList must reflect the rel content attribute.

relList’s DOMTokenList’s supported tokens are the keywords defined in HTML link types which are allowed on link elements and supported by the user agent.

rel’s supported tokens are the keywords defined in HTML link types which are allowed on link elements, impact the processing model, and are supported by the user agent. The possible supported tokens are alternate, icon, prefetch, stylesheet and next. rel’s supported tokens must only include the tokens from this list that the user agent implements the processing model for.

Other specifications may add HTML link types as defined in Other link types. These specifications may require that their link types be included in rel’s supported tokens.

The LinkStyle interface is also implemented by this element. [CSSOM]

Here, a set of link elements provide some style sheets:

<!-- a persistent style sheet -->
<link rel="stylesheet" href="default.css">

<!-- the preferred alternate style sheet -->
<link rel="stylesheet" href="green.css" title="Green styles">

<!-- some alternate style sheets -->
<link rel="alternate stylesheet" href="contrast.css" title="High contrast">
<link rel="alternate stylesheet" href="big.css" title="Big fonts">
<link rel="alternate stylesheet" href="wide.css" title="Wide screen">

The following example shows how you can specify versions of the page that use alternative formats, are aimed at other languages, and that are intended for other media:

<link rel=alternate href="/en/html" hreflang=en type=text/html title="English HTML">
<link rel=alternate href="/fr/html" hreflang=fr type=text/html title="French HTML">
<link rel=alternate href="/en/html/print" hreflang=en type=text/html media=print title="English HTML (for printing)">
<link rel=alternate href="/fr/html/print" hreflang=fr type=text/html media=print title="French HTML (for printing)">
<link rel=alternate href="/en/pdf" hreflang=en type=application/pdf title="English PDF">
<link rel=alternate href="/fr/pdf" hreflang=fr type=application/pdf title="French PDF">

4.2.5. The `meta` element

Metadata content.

If the itemprop attribute is present: flow content.

If the itemprop attribute is present: phrasing content.

If the charset attribute is present, or if the element’s http-equiv attribute is in the encoding declaration state: in a head element.

If the http-equiv attribute is present but not in the encoding declaration state: in a head element.

If the http-equiv attribute is present but not in the encoding declaration state: in a noscript element that is a child of a head element.

If the name attribute is present: where metadata content is expected.

If the itemprop attribute is present: where metadata content is expected.

If the itemprop attribute is present: where phrasing content is expected.

Nothing.

No end tag.

name — Metadata name

http-equiv — Pragma directive

content — Value of the element

charset — Character encoding declaration

Allowed ARIA role attribute values:

None