1. 4 The elements of HTML
    1. 4.1 The document element
      1. 4.1.1 The html element
    2. 4.2 Document metadata
      1. 4.2.1 The head element
      2. 4.2.2 The title element
      3. 4.2.3 The base element
      4. 4.2.4 The link element
        1. 4.2.4.1 Processing the media attribute
        2. 4.2.4.2 Processing the type attribute
        3. 4.2.4.3 Fetching and processing a resource from a link element
        4. 4.2.4.4 Processing `Link` headers
        5. 4.2.4.5 Early hints
        6. 4.2.4.6 Providing users with a means to follow hyperlinks created using the link element
      5. 4.2.5 The meta element
        1. 4.2.5.1 Standard metadata names
        2. 4.2.5.2 Other metadata names
        3. 4.2.5.3 Pragma directives
        4. 4.2.5.4 Specifying the document's character encoding
      6. 4.2.6 The style element
      7. 4.2.7 Interactions of styling and scripting

4 The elements of HTML

4.1 The document element

4.1.1 The html element

Element/html

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet ExplorerYes
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+

HTMLHtmlElement

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer5.5+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+
Categories:
None.
Contexts in which this element can be used:
As document's document element.
Wherever a subdocument fragment is allowed in a compound document.
Content model:
A head element followed by a body element.
Tag omission in text/html:
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.
Content attributes:
Global attributes
Accessibility considerations:
For authors.
For implementers.
DOM interface:
[Exposed=Window]
interface HTMLHtmlElement : HTMLElement {
  [HTMLConstructor] constructor();

  // also has obsolete members
};

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 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

Element/head

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera?Edge79+
Edge (Legacy)12+Internet ExplorerYes
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

HTMLHeadElement

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer5.5+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+
Categories:
None.
Contexts in which this element can be used:
As the first element in an html element.
Content model:
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.
Tag omission in text/html:
A head element's start tag can 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 can be omitted if the head element is not immediately followed by ASCII whitespace or a comment.
Content attributes:
Global attributes
Accessibility considerations:
For authors.
For implementers.
DOM interface:
[Exposed=Window]
interface HTMLHeadElement : HTMLElement {
  [HTMLConstructor] constructor();
};

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 lang=en>
 <head>
  <title>A document with a short head</title>
 </head>
 <body>
 ...

Here is an example of a longer one:

<!DOCTYPE HTML>
<HTML LANG="EN">
 <HEAD>
  <META CHARSET="UTF-8">
  <BASE HREF="https://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 email when HTML is used as an email authoring format, the title element can be omitted.

4.2.2 The title element

Element/title

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera?Edge79+
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HTMLTitleElement

Support in all current engines.

Firefox1+Safari3+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer5.5+
Firefox Android?Safari iOS1+Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+
Categories:
Metadata content.
Contexts in which this element can be used:
In a head element containing no other title elements.
Content model:
Text that is not inter-element whitespace.
Tag omission in text/html:
Neither tag is omissible.
Content attributes:
Global attributes
Accessibility considerations:
For authors.
For implementers.
DOM interface:
[Exposed=Window]
interface HTMLTitleElement : HTMLElement {
  [HTMLConstructor] constructor();

  [CEReactions] 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 child text content of the element.

Can be set, to replace the element's children with the given value.

The text attribute's getter must return this title element's child text content.

The text attribute's setter must string replace all with the given value within this title element.

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>
    ...
  <h1>The Dances</h1>

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

Element/base

Support in all current engines.

Firefox1+Safari3+Chrome1+
Opera?Edge79+
Edge (Legacy)12+Internet ExplorerYes
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

HTMLBaseElement

Support in all current engines.

Firefox1+Safari3+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer5.5+
Firefox Android?Safari iOS1+Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+
Categories:
Metadata content.
Contexts in which this element can be used:
In a head element containing no other base elements.
Content model:
Nothing.
Tag omission in text/html:
No end tag.
Content attributes:
Global attributes
hrefDocument base URL
target — Default navigable for hyperlink navigation and form submission
Accessibility considerations:
For authors.
For implementers.
DOM interface:
[Exposed=Window]
interface HTMLBaseElement : HTMLElement {
  [HTMLConstructor] constructor();

  [CEReactions] attribute USVString href;
  [CEReactions] attribute DOMString target;
};

The base element allows authors to specify the document base URL for the purposes of parsing URLs, and the name of the default navigable 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 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 navigable target name or keyword, which specifies which navigable 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.

To get an element's target, given an a, area, or form element element, and an optional string-or-null target (default null), run these steps:

  1. If target is null, then:

    1. If element has a target attribute, then set target to that attribute's value.

    2. Otherwise, if element's node document contains a base element with a target attribute, set target to the value of the target attribute of the first such base element.

  2. If target is not null, and contains an ASCII tab or newline and a U+003C (<), then set target to "_blank".

  3. Return target.


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

To set the frozen base URL for an element element:

  1. Let document be element's node document.

  2. Let urlRecord be the result of parsing the value of element's href content attribute with document's fallback base URL, and document's character encoding. (Thus, the base element isn't affected by itself.)

  3. If any of the following are true:

    then set element's frozen base URL to document's fallback base URL and return.

  4. Set element's frozen base URL to urlRecord.

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

  1. Let document be element's node document.

  2. Let url be the value of the href attribute of this element, if it has one, and the empty string otherwise.

  3. Let urlRecord be the result of parsing url with document's fallback base URL, and document's character encoding. (Thus, the base element isn't affected by other base elements or itself.)

  4. If urlRecord is failure, return url.

  5. Return the serialization of urlRecord.

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 lang="en">
    <head>
        <title>This is an example for the &lt;base&gt; element</title>
        <base href="https://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 "https://www.example.com/news/archives.html".

Element/link

Support in all current engines.

Firefox1+Safari4+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet ExplorerYes
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+

HTMLLinkElement

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer5.5+
Firefox Android?Safari iOS?Chrome Android?WebView Android37+Samsung Internet?Opera Android12.1+
Categories:
Metadata content.
If the element is allowed in the body: flow content.
If the element is allowed in the body: phrasing content.
Contexts in which this element can be used:
Where metadata content is expected.
In a noscript element that is a child of a head element.
If the element is allowed in the body: where phrasing content is expected.
Content model:
Nothing.
Tag omission in text/html:
No end tag.
Content attributes:
Global attributes
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
integrity — Integrity metadata used in Subresource Integrity checks [SRI]
hreflang — Language of the linked resource
type — Hint for the type of the referenced resource
referrerpolicyReferrer policy for fetches initiated by the element
sizes — Sizes of the icons (for rel="icon")
imagesrcset — Images to use in different situations, e.g., high-resolution displays, small monitors, etc. (for rel="preload")
imagesizes — Image sizes for different page layouts (for rel="preload")
asPotential destination for a preload request (for rel="preload" and rel="modulepreload")
blocking — Whether the element is potentially render-blocking
color — Color to use when customizing a site's icon (for rel="mask-icon")
disabled — Whether the link is disabled
fetchpriority — Sets the priority for fetches initiated by the element
Also, the title attribute has special semantics on this element: Title of the link; CSS style sheet set name
Accessibility considerations:
For authors.
For implementers.
DOM interface:
[Exposed=Window]
interface HTMLLinkElement : HTMLElement {
  [HTMLConstructor] constructor();

  [CEReactions] attribute USVString href;
  [CEReactions] attribute DOMString? crossOrigin;
  [CEReactions] attribute DOMString rel;
  [CEReactions] attribute DOMString as;
  [SameObject, PutForwards=value] readonly attribute DOMTokenList relList;
  [CEReactions] attribute DOMString media;
  [CEReactions] attribute DOMString integrity;
  [CEReactions] attribute DOMString hreflang;
  [CEReactions] attribute DOMString type;
  [SameObject, PutForwards=value] readonly attribute DOMTokenList sizes;
  [CEReactions] attribute USVString imageSrcset;
  [CEReactions] attribute DOMString imageSizes;
  [CEReactions] attribute DOMString referrerPolicy;
  [SameObject, PutForwards=value] readonly attribute DOMTokenList blocking;
  [CEReactions] attribute boolean disabled;
  [CEReactions] attribute DOMString fetchPriority;

  // also has obsolete members
};
HTMLLinkElement includes LinkStyle;

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

The address of the link(s) is given by the href attribute. If the href attribute is present, then its value must be a valid non-empty URL potentially surrounded by spaces. One or both of the href or imagesrcset attributes must be present.

If both the href and imagesrcset attributes are absent, then the element does not define a link.

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 unordered set of unique 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.

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, dns-prefetch, icon, manifest, modulepreload, next, pingback, preconnect, prefetch, preload, search, and stylesheet. rel's supported tokens must only include the tokens from this list that the user agent implements the processing model for.

Theoretically a user agent could support the processing model for the canonical keyword — if it were a search engine that executed JavaScript. But in practice that's quite unlikely. So in most cases, canonical ought not be included in rel's supported tokens.

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

If a link element has an itemprop attribute, or has a rel attribute that contains only keywords that are body-ok, then the element is said to be allowed in the body. This means that the element can be used where phrasing content is expected.

If the rel attribute is used, the element can only sometimes be used in the body of the page. 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.


Two categories of links can be created using the link element: links to external resources and hyperlinks. The 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.

Hyperlinks created with the link element and its rel attribute apply to the whole document. 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.

Unlike those created by a and area elements, hyperlinks created by link elements are not displayed as part of the document by default, in user agents that support the suggested default rendering. And even if they are force-displayed using CSS, they have no activation behavior. Instead, they primarily provide semantic information which might be used by the page or by other software that consumes the page's contents. Additionally, the user agent can provide its own UI for following such hyperlinks.

The exact behavior for links to external resources depends on the exact relationship, as defined for the relevant link type.


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

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

Subresource_Integrity

Support in all current engines.

Firefox43+Safari11.1+Chrome45+
Opera?Edge79+
Edge (Legacy)17+Internet ExplorerNo
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

The integrity attribute represents the integrity metadata for requests which this element is responsible for. The value is text. The attribute must only be specified on link elements that have a rel attribute that contains the stylesheet, preload, or modulepreload keyword. [SRI]

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 string.

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.

The referrerpolicy attribute is a referrer policy attribute. It is intended for use with external resource links, where it helps set the referrer policy used when fetching and processing the linked resource. [REFERRERPOLICY].

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 that are in a document tree, for which the title attribute defines CSS 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 imagesrcset attribute may be present, and is a srcset attribute.

The imagesrcset and href attributes (if width descriptors are not used) together contribute the image sources to the source set.

If the imagesrcset attribute is present and has any image candidate strings using a width descriptor, the imagesizes attribute must also be present, and is a sizes attribute. The imagesizes attribute contributes the source size to the source set.

The imagesrcset and imagesizes attributes must only be specified on link elements that have both a rel attribute that specifies the preload keyword, as well as an as attribute in the "image" state.

These attributes allow preloading the appropriate resource that is later used by an img element that has the corresponding values for its srcset and sizes attributes:

<link rel="preload" as="image"
      imagesrcset="wolf_400px.jpg 400w, wolf_800px.jpg 800w, wolf_1600px.jpg 1600w"
      imagesizes="50vw">

<!-- ... later, or perhaps inserted dynamically ... -->
<img src="wolf.jpg" alt="A rad wolf"
     srcset="wolf_400px.jpg 400w, wolf_800px.jpg 800w, wolf_1600px.jpg 1600w"
     sizes="50vw">

Note how we omit the href attribute, as it would only be relevant for browsers that do not support imagesrcset, and in those cases it would likely cause the incorrect image to be preloaded.

The imagesrcset attribute can be combined with the media attribute to preload the appropriate resource selected from a picture element's sources, for art direction:

<link rel="preload" as="image"
      imagesrcset="dog-cropped-1x.jpg, dog-cropped-2x.jpg 2x"
      media="(max-width: 800px)">
<link rel="preload" as="image"
      imagesrcset="dog-wide-1x.jpg, dog-wide-2x.jpg 2x"
      media="(min-width: 801px)">

<!-- ... later, or perhaps inserted dynamically ... -->
<picture>
  <source srcset="dog-cropped-1x.jpg, dog-cropped-2x.jpg 2x"
          media="(max-width: 800px)">
  <img src="dog-wide-1x.jpg" srcset="dog-wide-2x.jpg 2x"
       alt="An awesome dog">
</picture>

The sizes attribute gives the sizes of icons for visual media. Its value, if present, is merely advisory. User agents may use the value to decide which icon(s) to use if multiple icons are available. If specified, the attribute must have a value that is an unordered set of unique space-separated tokens which are ASCII case-insensitive. Each value must be either an ASCII case-insensitive match for the string "any", or a value that consists of two valid non-negative integers that do not have a leading U+0030 DIGIT ZERO (0) character and that are separated by a single U+0078 LATIN SMALL LETTER X or U+0058 LATIN CAPITAL LETTER X character. The attribute must only be specified on link elements that have a rel attribute that specifies the icon keyword or the apple-touch-icon keyword.

The apple-touch-icon keyword is a registered extension to the predefined set of link types, but user agents are not required to support it in any way.


The as attribute specifies the potential destination for a preload request for the resource given by the href attribute. It is an enumerated attribute. Each potential destination is a keyword for this attribute, mapping to a state of the same name. The attribute must be specified on link elements that have a rel attribute that contains the preload keyword. It may be specified on link elements that have a rel attribute that contains the modulepreload keyword; in such cases it must have a value which is a script-like destination. For other link elements, it must not be specified.

The processing model for how the as attribute is used is given in an individual link type's fetch and process the linked resource algorithm.

The attribute does not have a missing value default or invalid value default, meaning that invalid or missing values for the attribute map to no state. This is accounted for in the processing model. For preload links, both conditions are an error; for modulepreload links, a missing value will be treated as "script".


The blocking attribute is a blocking attribute. It is used by link type stylesheet, and it must only be specified on link elements that have a rel attribute containing that keyword.


The color attribute is used with the mask-icon link type. The attribute must only be specified on link elements that have a rel attribute that contains the mask-icon keyword. The value must be a string that matches the CSS <color> production, defining a suggested color that user agents can use to customize the display of the icon that the user sees when they pin your site.

This specification does not have any user agent requirements for the color attribute.

The mask-icon keyword is a registered extension to the predefined set of link types, but user agents are not required to support it in any way.


link elements have an associated explicitly enabled boolean. It is initially false.

The disabled attribute is a boolean attribute that is used with the stylesheet link type. The attribute must only be specified on link elements that have a rel attribute that contains the stylesheet keyword.

Whenever the disabled attribute is removed, set the link element's explicitly enabled attribute to true.

Removing the disabled attribute dynamically, e.g., using document.querySelector("link").removeAttribute("disabled"), will fetch and apply the style sheet:

<link disabled rel="alternate stylesheet" href="css/pooh">

HTMLLinkElement/fetchPriority

FirefoxNoSafari🔰 preview+Chrome102+
Opera?Edge102+
Edge (Legacy)?Internet ExplorerNo
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

The fetchpriority attribute is a fetch priority attribute that is intended for use with external resource links, where it is used to set the priority used when fetching and processing the linked resource.


HTMLLinkElement/rel

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer5.5+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+

The IDL attributes href, hreflang, integrity, media, rel, sizes, type, blocking, and disabled each must reflect the respective content attributes of the same name.

There is no reflecting IDL attribute for the color attribute, but this might be added later.

HTMLLinkElement/as

Support in all current engines.

Firefox56+Safari10+Chrome50+
Opera?Edge79+
Edge (Legacy)17+Internet ExplorerNo
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

The as IDL attribute must reflect the as content attribute, limited to only known values.

The crossOrigin IDL attribute must reflect the crossorigin content attribute, limited to only known values.

HTMLLinkElement/referrerPolicy

Support in all current engines.

Firefox50+Safari14.1+Chrome58+
Opera?Edge79+
Edge (Legacy)?Internet ExplorerNo
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

The referrerPolicy IDL attribute must reflect the referrerpolicy content attribute, limited to only known values.

The fetchPriority IDL attribute must reflect the fetchpriority content attribute, limited to only known values.

The imageSrcset IDL attribute must reflect the imagesrcset content attribute.

The imageSizes IDL attribute must reflect the imagesizes content attribute.

HTMLLinkElement/relList

Support in all current engines.

Firefox30+Safari9+Chrome50+
Opera?Edge79+
Edge (Legacy)17+Internet ExplorerNo
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

The relList IDL attribute must reflect the rel content attribute.

The relList attribute can be used for feature detection, by calling its supports() method to check which types of links are supported.

4.2.4.1 Processing the media attribute

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

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.

4.2.4.2 Processing the type attribute

If the type 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 string, 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 UA does not support the given MIME type for the given link relationship, then the UA should not fetch and process the linked resource; if the UA does support the given MIME type for the given link relationship, then the UA should fetch and process the linked 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 fetch and process the linked resource if the type was known and supported, then the user agent should fetch and process the linked 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.

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 UA 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 default fetch and process the linked resource, given a link element el, is as follows:

  1. Let options be the result of creating link options from el.

  2. Let request be the result of creating a link request given options.

  3. If request is null, then return.

  4. Set request's synchronous flag.

  5. Run the linked resource fetch setup steps, given el and request. If the result is false, then return.

  6. Set request's initiator type to "css" if el's rel attribute contains the keyword stylesheet; "link" otherwise.

  7. Fetch request with processResponseConsumeBody set to the following steps given response response and null, failure, or a byte sequence bodyBytes:

    1. Let success be true.

    2. If any of the following are true:

      then set success to false.

      Note that content-specific errors, e.g., CSS parse errors or PNG decoding errors, do not affect success.

    3. Otherwise, wait for the link resource's critical subresources to finish loading.

      The specification that defines a link type's critical subresources (e.g., CSS) is expected to describe how these subresources are fetched and processed. However, since this is not currently explicit, this specification describes waiting for a link resource's critical subresources to be fetched and processed, with the expectation that this will be done correctly.

    4. Process the linked resource given el, success, response, and bodyBytes.

To create a link request given a link processing options options:

  1. Assert: options's href is not the empty string.

  2. If options's destination is not a destination, then return null.

  3. Let url be the result of encoding-parsing a URL given options's href, relative to options's base URL.

    Passing the base URL instead of a document or environment is tracked by issue #9715.

  4. If url is failure, then return null.

  5. Let request be the result of creating a potential-CORS request given url, options's destination, and options's crossorigin.

  6. Set request's policy container to options's policy container.

  7. Set request's integrity metadata to options's integrity.

  8. Set request's cryptographic nonce metadata to options's cryptographic nonce metadata.

  9. Set request's referrer policy to options's referrer policy.

  10. Set request's client to options's environment.

  11. Set request's priority to options's fetch priority.

  12. Return request.

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

Similar to the fetch and process the linked resource algorithm, all external resource links have a process the linked resource algorithm which takes a link element el, boolean success, a response response, and a byte sequence bodyBytes. Individual link types may provide their own process the linked resource algorithm, but unless explicitly stated, that algorithm does nothing.

Unless otherwise specified for a given rel keyword, the element must delay the load event of the element's node document until all the attempts to fetch and process the linked resource and its critical subresources are complete. (Resources that the user agent has not yet attempted to fetch and process, e.g., because it is waiting for the resource to be needed, do not delay the load event.)

All link types that can be external resource links define a process a link header algorithm, which takes a link processing options. This algorithm defines whether and how they react to appearing in an HTTP `Link` response header.

For most link types, this algorithm does nothing. The summary table is a good reference to quickly know whether a link type has defined process a link header steps.

A link processing options is a struct. It has the following items:

href (default the empty string)
destination (default the empty string)
initiator (default "link")
integrity (default the empty string)
type (default the empty string)
cryptographic nonce metadata (default the empty string)
A string
crossorigin (default No CORS)
A CORS settings attribute state
referrer policy (default the empty string)
A referrer policy
source set (default null)
Null or a source set
base URL
A URL
origin
An origin
environment
An environment
policy container
A policy container
document (default null)
Null or a Document
on document ready (default null)
Null or an algorithm accepting a Document
fetch priority (default auto)
A fetch priority attribute state

A link processing options has a base URL and an href rather than a parsed URL because the URL could be a result of the options's source set.

To create link options from element given a link element el:

  1. Let document be el's node document.

  2. Let options be a new link processing options with

    destination
    the result of translating the state of el's as attribute
    crossorigin
    the state of el's crossorigin content attribute
    referrer policy
    the state of el's referrerpolicy content attribute
    source set
    el's source set
    base URL
    document's document base URL
    origin
    document's origin
    environment
    document's relevant settings object
    policy container
    document's policy container
    document
    document
    cryptographic nonce metadata
    The current value of el's [[CryptographicNonce]] internal slot
    fetch priority
    the state of el's fetchpriority content attribute
  3. If el has an href attribute, then set options's href to the value of el's href attribute.

  4. If el has an integrity attribute, then set options's integrity to the value of el's integrity content attribute.

  5. If el has a type attribute, then set options's type to the value of el's type attribute.

  6. Assert: options's href is not the empty string, or options's source set is not null.

    A link element with neither an href or an imagesrcset does not represent a link.

  7. Return options.

To extract links from headers given a header list headers:

  1. Let links be a new list.

  2. Let rawLinkHeaders be the result of getting, decoding, and splitting `Link` from response's header list.

  3. For each linkHeader of rawLinkHeaders:

    1. Let linkObject be the result of parsing linkHeader. [WEBLINK]

    2. If linkObject["target_uri"] does not exist, then continue.

    3. Append linkObject to links.

  4. Return links.

To process link headers given a Document doc, a response response, and a "pre-media" or "media" phase:

  1. Let links be the result of extracting links from response's header list.

  2. For each linkObject in links:

    1. Let rel be linkObject["relation_type"].

    2. Let attribs be linkObject["target_attributes"].

    3. Let expectedPhase be "media" if either "srcset", "imagesrcset", or "media" exist in attribs; otherwise "pre-media".

    4. If expectedPhase is not phase, then continue.

    5. If attribs["media"] exists and attribs["media"] does not match the environment, then continue.

    6. Let options be a new link processing options with

      href
      linkObject["target_uri"]
      base URL
      doc's document base URL
      origin
      doc's origin
      environment
      doc's relevant settings object
      policy container
      doc's policy container
      document
      doc
    7. Apply link options from parsed header attributes to options given attribs.

    8. If attribs["imagesrcset"] exists and attribs["imagesizes"] exists, then set options's source set to the result of creating a source set given linkObject["target_uri"], attribs["imagesrcset"], attribs["imagesizes"], and null.

    9. Run the process a link header steps for rel given options.

To apply link options from parsed header attributes to a link processing options options given attribs:

  1. If attribs["as"] exists, then set options's destination to the result of translating attribs["as"].

  2. If attribs["crossorigin"] exists and is an ASCII case-insensitive match for one of the CORS settings attribute keywords, then set options's crossorigin to the CORS settings attribute state corresponding to that keyword.

  3. If attribs["integrity"] exists, then set options's integrity to attribs["integrity"].

  4. If attribs["referrerpolicy"] exists and is an ASCII case-insensitive match for some referrer policy, then set options's referrer policy to that referrer policy.

  5. If attribs["nonce"] exists, then set options's nonce to attribs["nonce"].

  6. If attribs["type"] exists, then set options's type to attribs["type"].

  7. If attribs["fetchpriority"] exists and is an ASCII case-insensitive match for a fetch priority attribute keyword, then set options's fetch priority to that fetch priority attribute keyword.

4.2.4.5 Early hints

Status/103

Firefoxpreview+SafariNoChrome103+
OperaNoEdge103+
Edge (Legacy)?Internet ExplorerNo
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

Early hints allow user-agents to perform some operations, such as to speculatively load resources that are likely to be used by the document, before the navigation request is fully handled by the server and a response code is served. Servers can indicate early hints by serving a response with a 103 status code before serving the final response.[RFC8297]

For compatibility reasons early hints are typically delivered over HTTP/2 or above, but for readability we use HTTP/1.1-style notation below.

For example, given the following sequence of responses:

103 Early Hint
Link: </image.png>; rel=preload; as=image
200 OK
Content-Type: text/html

<!DOCTYPE html>
...
<img src="/image.png">

the image will start loading before the HTML content arrives.

Only the first early hint response served during the navigation is handled, and it is discarded if it is succeeded by a cross-origin redirect.

In addition to the `Link` headers, it is possible that the 103 response contains a Content Security Policy header, which is enforced when processing the early hint.

For example, given the following sequence of responses:

103 Early Hint
Content-Security-Policy: style-src: self;
Link: </style.css>; rel=preload; as=style
103 Early Hint
Link: </image.png>; rel=preload; as=image
302 Redirect
Location: /alternate.html
200 OK
Content-Security-Policy: style-src: none;
Link: </font.ttf>; rel=preload; as=font

The font and style would be loaded, and the image will be discarded, as only the first early hint response in the final redirect chain is respected. The late Content Security Policy header comes after the request to fetch the style has already been performed, but the style will not be accessible to the document.

To process early hint headers given a response response and an environment reservedEnvironment:

Early-hint `Link` headers are always processed before `Link` headers from the final response, followed by link elements. This is equivalent to prepending the contents of the early and final `Link` headers to the Document's head element, in respective order.

  1. Let earlyPolicyContainer be the result of creating a policy container from a fetch response given response and reservedEnvironment.

    This allows the early hint response to include a Content Security Policy which would be enforced when fetching the early hint request.

  2. Let links be the result of extracting links from response's header list.

  3. Let earlyHints be an empty list.

  4. For each linkObject in links:

    The moment we receive the early hint link header, we begin fetching earlyRequest. If it comes back before the Document is created, we set earlyResponse to the response of that fetch and once the Document is created we commit it (by making it available in the map of preloaded resources as if it was a link element). If the Document is created first, the response is committed as soon as it becomes available.

    1. Let rel be linkObject["relation_type"].

    2. Let options be a new link processing options with

      href
      linkObject["target_uri"]
      initiator
      "early-hint"
      base URL
      response's URL
      origin
      response's URL's origin
      environment
      reservedEnvironment
      policy container
      earlyPolicyContainer
    3. Let attribs be linkObject["target_attributes"].

      Only the as, crossorigin, integrity, and type attributes are handled as part of early hint processing. The other ones, in particular blocking, imagesrcset, imagesizes, and media are only applicable once a Document is created.

    4. Apply link options from parsed header attributes to options given attribs.

    5. Run the process a link header steps for rel given options.

    6. Append options to earlyHints.

  5. Return the following substeps given Document doc: for each options in earlyHints:

    1. If options's on document ready is null, then set options's document to docs.

    2. Otherwise, call options's on document ready with doc.

Interactive user agents may provide users with a means to follow the hyperlinks created using the link element, somewhere within their user interface. Such invocations of the follow the hyperlink algorithm must set the userInvolvement argument to "browser UI". 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:

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

4.2.5 The meta element

Element/meta

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet ExplorerYes
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+

HTMLMetaElement

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer5.5+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+
Categories:
Metadata content.
If the itemprop attribute is present: flow content.
If the itemprop attribute is present: phrasing content.
Contexts in which this element can be used:
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.
Content model:
Nothing.
Tag omission in text/html:
No end tag.
Content attributes:
Global attributes
name — Metadata name
http-equiv — Pragma directive
content — Value of the element
charsetCharacter encoding declaration
media — Applicable media
Accessibility considerations:
For authors.
For implementers.
DOM interface:
[Exposed=Window]
interface HTMLMetaElement : HTMLElement {
  [HTMLConstructor] constructor();

  [CEReactions] attribute DOMString name;
  [CEReactions] attribute DOMString httpEquiv;
  [CEReactions] attribute DOMString content;
  [CEReactions] attribute DOMString media;

  // also has obsolete members
};

The meta element represents various kinds of metadata that cannot be expressed using the title, base, link, style, and script elements.

The meta element can represent document-level metadata with the name attribute, pragma directives with the http-equiv attribute, and the file's character encoding declaration when an HTML document is serialized to string form (e.g. for transmission over the network or for disk storage) with the charset attribute.

Exactly one of the name, http-equiv, charset, and itemprop attributes must be specified.

If either name, http-equiv, or itemprop is specified, then the content attribute must also be specified. Otherwise, it must be omitted.

The charset attribute specifies the character encoding used by the document. This is a character encoding declaration. If the attribute is present, its value must be an ASCII case-insensitive match for the string "utf-8".

The charset attribute on the meta element has no effect in XML documents, but is allowed in XML documents in order to facilitate migration to and from XML.

There must not be more than one meta element with a charset attribute per document.

The content attribute gives the value of the document metadata or pragma directive when the element is used for those purposes. The allowed values depend on the exact context, as described in subsequent sections of this specification.

If a meta element has a name attribute, it sets document metadata. Document metadata is expressed in terms of name-value pairs, the name attribute on the meta element giving the name, and the content attribute on the same element giving the value. The name specifies what aspect of metadata is being set; valid names and the meaning of their values are described in the following sections. If a meta element has no content attribute, then the value part of the metadata name-value pair is the empty string.

The media attribute says which media the metadata applies to. The value must be a valid media query list. Unless the name is theme-color, the media attribute has no effect on the processing model and must not be used by authors.

The name, content, and media IDL attributes must reflect the respective content attributes of the same name. The IDL attribute httpEquiv must reflect the content attribute http-equiv.

4.2.5.1 Standard metadata names

Element/meta/name

Support in all current engines.

Firefox1+Safari4+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer6+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+

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

Names are case-insensitive, and must be compared in an ASCII case-insensitive manner.

application-name

The value must be a short free-form string giving the name of the web application that the page represents. If the page is not a web application, the application-name metadata name must not be used. Translations of the web application's name may be given, using the lang attribute to specify the language of each name.

There must not be more than one meta element with a given language and where the name attribute value is an ASCII case-insensitive match for application-name per document.

User agents may use the application name in UI in preference to the page's title, since the title might include status messages and the like relevant to the status of the page at a particular moment in time instead of just being the name of the application.

To find the application name to use given an ordered list of languages (e.g. British English, American English, and English), user agents must run the following steps:

  1. Let languages be the list of languages.

  2. Let default language be the language of the Document's document element, if any, and if that language is not unknown.

  3. If there is a default language, and if it is not the same language as any of the languages in languages, append it to languages.

  4. Let winning language be the first language in languages for which there is a meta element in the Document where the name attribute value is an ASCII case-insensitive match for application-name and whose language is the language in question.

    If none of the languages have such a meta element, then return; there's no given application name.

  5. Return the value of the content attribute of the first meta element in the Document in tree order where the name attribute value is an ASCII case-insensitive match for application-name and whose language is winning language.

This algorithm would be used by a browser when it needs a name for the page, for instance, to label a bookmark. The languages it would provide to the algorithm would be the user's preferred languages.

author

The value must be a free-form string giving the name of one of the page's authors.

description

The value must be a free-form string that describes the page. The value must be appropriate for use in a directory of pages, e.g. in a search engine. There must not be more than one meta element where the name attribute value is an ASCII case-insensitive match for description per document.

generator

The value must be a free-form string that identifies one of the software packages used to generate the document. This value must not be used on pages whose markup is not generated by software, e.g. pages whose markup was written by a user in a text editor.

Here is what a tool called "Frontweaver" could include in its output, in the page's head element, to identify itself as the tool used to generate the page:

<meta name=generator content="Frontweaver 8.2">
keywords

The value must be a set of comma-separated tokens, each of which is a keyword relevant to the page.

This page about typefaces on British motorways uses a meta element to specify some keywords that users might use to look for the page:

<!DOCTYPE HTML>
<html lang="en-GB">
 <head>
  <title>Typefaces on UK motorways</title>
  <meta name="keywords" content="british,type face,font,fonts,highway,highways">
 </head>
 <body>
  ...

Many search engines do not consider such keywords, because this feature has historically been used unreliably and even misleadingly as a way to spam search engine results in a way that is not helpful for users.

To obtain the list of keywords that the author has specified as applicable to the page, the user agent must run the following steps:

  1. Let keywords be an empty list.

  2. For each meta element with a name attribute and a content attribute and where the name attribute value is an ASCII case-insensitive match for keywords:

    1. Split the value of the element's content attribute on commas.

    2. Add the resulting tokens, if any, to keywords.

  3. Remove any duplicates from keywords.

  4. Return keywords. This is the list of keywords that the author has specified as applicable to the page.

User agents should not use this information when there is insufficient confidence in the reliability of the value.

For instance, it would be reasonable for a content management system to use the keyword information of pages within the system to populate the index of a site-specific search engine, but a large-scale content aggregator that used this information would likely find that certain users would try to game its ranking mechanism through the use of inappropriate keywords.

referrer

The value must be a referrer policy, which defines the default referrer policy for the Document. [REFERRERPOLICY]

If any meta element element is inserted into the document, or has its name or content attributes changed, user agents must run the following algorithm:

  1. If element is not in a document tree, then return.

  2. If element does not have a name attribute whose value is an ASCII case-insensitive match for "referrer", then return.

  3. If element does not have a content attribute, or that attribute's value is the empty string, then return.

  4. Let value be the value of element's content attribute, converted to ASCII lowercase.

  5. If value is one of the values given in the first column of the following table, then set value to the value given in the second column:

    Legacy value Referrer policy
    never no-referrer
    default the default referrer policy
    always unsafe-url
    origin-when-crossorigin origin-when-cross-origin
  6. If value is a referrer policy, then set element's node document's policy container's referrer policy to policy.

For historical reasons, unlike other standard metadata names, the processing model for referrer is not responsive to element removals, and does not use tree order. Only the most-recently-inserted or most-recently-modified meta element in this state has an effect.

theme-color

Element/meta/name/theme-color

FirefoxNoSafari15+Chrome🔰 73+
OperaNoEdge🔰 79+
Edge (Legacy)?Internet ExplorerNo
Firefox Android?Safari iOS?Chrome Android80+WebView AndroidNoSamsung Internet6.2+Opera AndroidNo

The value must be a string that matches the CSS <color> production, defining a suggested color that user agents should use to customize the display of the page or of the surrounding user interface. For example, a browser might color the page's title bar with the specified value, or use it as a color highlight in a tab bar or task switcher.

Within an HTML document, the media attribute value must be unique amongst all the meta elements with their name attribute value set to an ASCII case-insensitive match for theme-color.

This standard itself uses "WHATWG green" as its theme color:

<!DOCTYPE HTML>
<title>HTML Standard</title>
<meta name="theme-color" content="#3c790a">
...

The media attribute may be used to describe the context in which the provided color should be used.

If we only wanted to use "WHATWG green" as this standard's theme color in dark mode, we could use the prefers-color-scheme media feature:

<!DOCTYPE HTML>
<title>HTML Standard</title>
<meta name="theme-color" content="#3c790a" media="(prefers-color-scheme: dark)">
...

To obtain a page's theme color, user agents must run the following steps:

  1. Let candidate elements be the list of all meta elements that meet the following criteria, in tree order:

  2. For each element in candidate elements:

    1. If element has a media attribute and the value of element's media attribute does not match the environment, then continue.

    2. Let value be the result of stripping leading and trailing ASCII whitespace from the value of element's content attribute.

    3. Let color be the result of parsing value.

    4. If color is not failure, then return color.

  3. Return nothing (the page has no theme color).

If any meta elements are inserted into the document or removed from the document, or existing meta elements have their name, content, or media attributes changed, or if the environment changes such that any meta element's media attribute's value may now or may no longer match the environment, user agents must re-run the above algorithm and apply the result to any affected UI.

When using the theme color in UI, user agents may adjust it in implementation-specific ways to make it more suitable for the UI in question. For example, if a user agent intends to use the theme color as a background and display white text over it, it might use a darker variant of the theme color in that part of the UI, to ensure adequate contrast.

color-scheme

To aid user agents in rendering the page background with the desired color scheme immediately (rather than waiting for all CSS in the page to load), a 'color-scheme' value can be provided in a meta element.

The value must be a string that matches the syntax for the CSS 'color-scheme' property value. It determines the page's supported color-schemes.

There must not be more than one meta element with its name attribute value set to an ASCII case-insensitive match for color-scheme per document.

The following declaration indicates that the page is aware of and can handle a color scheme with dark background colors and light foreground colors:

<meta name="color-scheme" content="dark">

To obtain a page's supported color-schemes, user agents must run the following steps:

  1. Let candidate elements be the list of all meta elements that meet the following criteria, in tree order:

  2. For each element in candidate elements:

    1. Let parsed be the result of parsing a list of component values given the value of element's content attribute.
    2. If parsed is a valid CSS 'color-scheme' property value, then return parsed.
  3. Return null.

If any meta elements are inserted into the document or removed from the document, or existing meta elements have their name or content attributes changed, user agents must re-run the above algorithm.

Because these rules check successive elements until they find a match, an author can provide multiple such values to handle fallback for legacy user agents. Opposite to how CSS fallback works for properties, the multiple meta elements needs to be arranged with the legacy values after the newer values.

4.2.5.2 Other metadata names

Anyone can create and use their own extensions to the predefined set of metadata names. There is no requirement to register such extensions.

However, a new metadata name should not be created in any of the following cases:

Also, before creating and using a new metadata name, consulting the WHATWG Wiki MetaExtensions page is encouraged — to avoid choosing a metadata name that's already in use, and to avoid duplicating the purpose of any metadata names that are already in use, and to avoid new standardized names clashing with your chosen name. [WHATWGWIKI]

Anyone is free to edit the WHATWG Wiki MetaExtensions page at any time to add a metadata name. New metadata names can 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 non-normative description of what the metadata name's meaning is, including the format the value is required to be in.

Specification
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). Anyone may remove synonyms that are not used in practice; only names that need to be processed as synonyms for compatibility with legacy content are to be registered in this way.

Status

One of the following:

Proposed
The name has not received wide peer review and approval. Someone has proposed it and is, or soon will be, using it.
Ratified
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.
Discontinued
The metadata name has received wide peer review and it has been found wanting. Existing pages are using this metadata name, but new pages should avoid it. The "brief description" and "specification" entries will give details of what authors should use instead, if anything.

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

If a metadata name is added in the "proposed" state for a period of a month or more without being used or specified, then it may be removed from the WHATWG Wiki MetaExtensions page.

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

Anyone can change the status at any time, but should only do so in accordance with the definitions above.

4.2.5.3 Pragma directives

When the http-equiv attribute is specified on a meta element, the element is a pragma directive.

The http-equiv attribute is an enumerated attribute with the following keywords and states:

Keyword Conforming State Brief description
content-language No Content language Sets the pragma-set default language.
content-type Encoding declaration An alternative form of setting the charset.
default-style Default style Sets the name of the default CSS style sheet set.
refresh Refresh Acts as a timed redirect.
set-cookie No Set-Cookie Has no effect.
x-ua-compatible X-UA-Compatible In practice, encourages Internet Explorer to more closely follow the specifications.
content-security-policy Content security policy Enforces a Content Security Policy on a Document.

When a meta element is inserted into the document, if its http-equiv attribute is present and represents one of the above states, then the user agent must run the algorithm appropriate for that state, as described in the following list:

Content language state (http-equiv="content-language")

This feature is non-conforming. Authors are encouraged to use the lang attribute instead.

This pragma sets the pragma-set default language. Until such a pragma is successfully processed, there is no pragma-set default language.

  1. If the meta element has no content attribute, then return.

  2. If the element's content attribute contains a U+002C COMMA character (,) then return.

  3. Let input be the value of the element's content attribute.

  4. Let position point at the first character of input.

  5. Skip ASCII whitespace within input given position.

  6. Collect a sequence of code points that are not ASCII whitespace from input given position.

  7. Let candidate be the string that resulted from the previous step.

  8. If candidate is the empty string, return.

  9. Set the pragma-set default language to candidate.

    If the value consists of multiple space-separated tokens, tokens after the first are ignored.

This pragma is almost, but not quite, entirely unlike the HTTP `Content-Language` header of the same name. [HTTP]

Encoding declaration state (http-equiv="content-type")

The Encoding declaration state is just an alternative form of setting the charset attribute: it is a character encoding declaration. This state's user agent requirements are all handled by the parsing section of the specification.

For meta elements with an http-equiv attribute in the Encoding declaration state, the content attribute must have a value that is an ASCII case-insensitive match for a string that consists of: the literal string "text/html;", optionally followed by any number of ASCII whitespace, followed by the literal string "charset=utf-8".

A document must not contain both a meta element with an http-equiv attribute in the Encoding declaration state and a meta element with the charset attribute present.

The Encoding declaration state may be used in HTML documents, but elements with an http-equiv attribute in that state must not be used in XML documents.

Default style state (http-equiv="default-style")

Alternative_style_sheets

Support in one engine only.

Firefox3+Safari?Chrome1–48
OperaYesEdgeNo
Edge (Legacy)?Internet Explorer8+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

This pragma sets the name of the default CSS style sheet set.

  1. If the meta element has no content attribute, or if that attribute's value is the empty string, then return.

  2. Change the preferred CSS style sheet set name with the name being the value of the element's content attribute. [CSSOM]

Refresh state (http-equiv="refresh")

This pragma acts as a timed redirect.

A Document object has an associated will declaratively refresh (a boolean). It is initially false.

  1. If the meta element has no content attribute, or if that attribute's value is the empty string, then return.

  2. Let input be the value of the element's content attribute.

  3. Run the shared declarative refresh steps with the meta element's node document, input, and the meta element.

The shared declarative refresh steps, given a Document object document, string input, and optionally a meta element meta, are as follows:

  1. If document's will declaratively refresh is true, then return.

  2. Let position point at the first code point of input.

  3. Skip ASCII whitespace within input given position.

  4. Let time be 0.

  5. Collect a sequence of code points that are ASCII digits from input given position, and let the result be timeString.

  6. If timeString is the empty string, then:

    1. If the code point in input pointed to by position is not U+002E (.), then return.

  7. Otherwise, set time to the result of parsing timeString using the rules for parsing non-negative integers.

  8. Collect a sequence of code points that are ASCII digits and U+002E FULL STOP characters (.) from input given position. Ignore any collected characters.

  9. Let urlRecord be document's URL.

  10. If position is not past the end of input, then:

    1. If the code point in input pointed to by position is not U+003B (;), U+002C (,), or ASCII whitespace, then return.

    2. Skip ASCII whitespace within input given position.

    3. If the code point in input pointed to by position is U+003B (;) or U+002C (,), then advance position to the next code point.

    4. Skip ASCII whitespace within input given position.

  11. If position is not past the end of input, then:

    1. Let urlString be the substring of input from the code point at position to the end of the string.

    2. If the code point in input pointed to by position is U+0055 (U) or U+0075 (u), then advance position to the next code point. Otherwise, jump to the step labeled skip quotes.

    3. If the code point in input pointed to by position is U+0052 (R) or U+0072 (r), then advance position to the next code point. Otherwise, jump to the step labeled parse.

    4. If the code point in input pointed to by position is U+004C (L) or U+006C (l), then advance position to the next code point. Otherwise, jump to the step labeled parse.

    5. Skip ASCII whitespace within input given position.

    6. If the code point in input pointed to by position is U+003D (=), then advance position to the next code point. Otherwise, jump to the step labeled parse.

    7. Skip ASCII whitespace within input given position.

    8. Skip quotes: If the code point in input pointed to by position is U+0027 (') or U+0022 ("), then let quote be that code point, and advance position to the next code point. Otherwise, let quote be the empty string.

    9. Set urlString to the substring of input from the code point at position to the end of the string.

    10. If quote is not the empty string, and there is a code point in urlString equal to quote, then truncate urlString at that code point, so that it and all subsequent code points are removed.

    11. Parse: Set urlRecord to the result of encoding-parsing a URL given urlString, relative to document.

    12. If urlRecord is failure, then return.

  12. Set document's will declaratively refresh to true.

  13. Perform one or more of the following steps:

    • After the refresh has come due (as defined below), if the user has not canceled the redirect and, if meta is given, document's active sandboxing flag set does not have the sandboxed automatic features browsing context flag set, then navigate document's node navigable to urlRecord using document, with historyHandling set to "replace".

      For the purposes of the previous paragraph, a refresh is said to have come due as soon as the later of the following two conditions occurs:

      • At least time seconds have elapsed since document's completely loaded time, adjusted to take into account user or user agent preferences.
      • If meta is given, at least time seconds have elapsed since meta was inserted into the document document, adjusted to take into account user or user agent preferences.

      It is important to use document here, and not meta's node document, as that might have changed between the initial set of steps and the refresh coming due and meta is not always given (in case of the HTTP `Refresh` header).

    • Provide the user with an interface that, when selected, navigates document's node navigable to urlRecord using document.

    • Do nothing.

    In addition, the user agent may, as with anything, inform the user of any and all aspects of its operation, including the state of any timers, the destinations of any timed redirects, and so forth.

For meta elements with an http-equiv attribute in the Refresh state, the content attribute must have a value consisting either of:

In the former case, the integer represents a number of seconds before the page is to be reloaded; in the latter case the integer represents a number of seconds before the page is to be replaced by the page at the given URL.

A news organization's front page could include the following markup in the page's head element, to ensure that the page automatically reloads from the server every five minutes:

<meta http-equiv="Refresh" content="300">

A sequence of pages could be used as an automated slide show by making each page refresh to the next page in the sequence, using markup such as the following:

<meta http-equiv="Refresh" content="20; URL=page4.html">
Set-Cookie state (http-equiv="set-cookie")

This pragma is non-conforming and has no effect.

User agents are required to ignore this pragma.

X-UA-Compatible state (http-equiv="x-ua-compatible")

In practice, this pragma encourages Internet Explorer to more closely follow the specifications.

For meta elements with an http-equiv attribute in the X-UA-Compatible state, the content attribute must have a value that is an ASCII case-insensitive match for the string "IE=edge".

User agents are required to ignore this pragma.

Content security policy state (http-equiv="content-security-policy")

This pragma enforces a Content Security Policy on a Document. [CSP]

  1. If the meta element is not a child of a head element, return.

  2. If the meta element has no content attribute, or if that attribute's value is the empty string, then return.

  3. Let policy be the result of executing Content Security Policy's parse a serialized Content Security Policy algorithm on the meta element's content attribute's value, with a source of "meta", and a disposition of "enforce".

  4. Remove all occurrences of the report-uri, frame-ancestors, and sandbox directives from policy.

  5. Enforce the policy policy.

For meta elements with an http-equiv attribute in the Content security policy state, the content attribute must have a value consisting of a valid Content Security Policy, but must not contain any report-uri, frame-ancestors, or sandbox directives. The Content Security Policy given in the content attribute will be enforced upon the current document. [CSP]

At the time of inserting the meta element to the document, it is possible that some resources have already been fetched. For example, images might be stored in the list of available images prior to dynamically inserting a meta element with an http-equiv attribute in the Content security policy state. Resources that have already been fetched are not guaranteed to be blocked by a Content Security Policy that's enforced late.

A page might choose to mitigate the risk of cross-site scripting attacks by preventing the execution of inline JavaScript, as well as blocking all plugin content, using a policy such as the following:

<meta http-equiv="Content-Security-Policy" content="script-src 'self'; object-src 'none'">

There must not be more than one meta element with any particular state in the document at a time.

4.2.5.4 Specifying the document's character encoding

A character encoding declaration is a mechanism by which the character encoding used to store or transmit a document is specified.

The Encoding standard requires use of the UTF-8 character encoding and requires use of the "utf-8" encoding label to identify it. Those requirements necessitate that the document's character encoding declaration, if it exists, specifies an encoding label using an ASCII case-insensitive match for "utf-8". Regardless of whether a character encoding declaration is present or not, the actual character encoding used to encode the document must be UTF-8. [ENCODING]

To enforce the above rules, authoring tools must default to using UTF-8 for newly-created documents.

The following restrictions also apply:

In addition, due to a number of restrictions on meta elements, there can only be one meta-based character encoding declaration per document.

If an HTML document does not start with a BOM, and its encoding is not explicitly given by Content-Type metadata, and the document is not an iframe srcdoc document, then the encoding must be specified using a meta element with a charset attribute or a meta element with an http-equiv attribute in the Encoding declaration state.

A character encoding declaration is required (either in the Content-Type metadata or explicitly in the file) even when all characters are in the ASCII range, because a character encoding is needed to process non-ASCII characters entered by the user in forms, in URLs generated by scripts, and so forth.

Using non-UTF-8 encodings can have unexpected results on form submission and URL encodings, which use the document's character encoding by default.

If the document is an iframe srcdoc document, the document must not have a character encoding declaration. (In this case, the source is already decoded, since it is part of the document that contained the iframe.)

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

In HTML, to declare that the character encoding is UTF-8, the author could include the following markup near the top of the document (in the head element):

<meta charset="utf-8">

In XML, the XML declaration would be used instead, at the very top of the markup:

<?xml version="1.0" encoding="utf-8"?>

4.2.6 The style element

Element/style

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera3.5+Edge79+
Edge (Legacy)12+Internet Explorer3+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android10.1+

HTMLStyleElement

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer5.5+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+
Categories:
Metadata content.
Contexts in which this element can be used:
Where metadata content is expected.
In a noscript element that is a child of a head element.
Content model:
Text that gives a conformant style sheet.
Tag omission in text/html:
Neither tag is omissible.
Content attributes:
Global attributes
media — Applicable media
blocking — Whether the element is potentially render-blocking
Also, the title attribute has special semantics on this element: CSS style sheet set name
Accessibility considerations:
For authors.
For implementers.
DOM interface:
[Exposed=Window]
interface HTMLStyleElement : HTMLElement {
  [HTMLConstructor] constructor();

  attribute boolean disabled;
  [CEReactions] attribute DOMString media;
  [SameObject, PutForwards=value] readonly attribute DOMTokenList blocking;

  // also has obsolete members
};
HTMLStyleElement includes LinkStyle;

The style element allows authors to embed CSS style sheets in their documents. The style element is one of several inputs to the styling processing model. The element does not represent content for the user.

HTMLStyleElement/disabled

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)13+Internet Explorer5.5+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+

The disabled getter steps are:

  1. If this does not have an associated CSS style sheet, return false.

  2. If this's associated CSS style sheet's disabled flag is set, return true.

  3. Return false.

The disabled setter steps are:

  1. If this does not have an associated CSS style sheet, return.

  2. If the given value is true, set this's associated CSS style sheet's disabled flag. Otherwise, unset this's associated CSS style sheet's disabled flag.

Importantly, disabled attribute assignments only take effect when the style element has an associated CSS style sheet:

const style = document.createElement('style');
style.disabled = true;
style.textContent = 'body { background-color: red; }';
document.body.append(style);
console.log(style.disabled); // false

The media attribute says which media the styles apply to. The value must be a valid media query list. The user agent must apply the styles when the media attribute's value matches the environment and the other relevant conditions apply, and must not apply them otherwise.

The styles might be further limited in scope, e.g. in CSS with the use of @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 styles apply to all media.

The blocking attribute is a blocking attribute.

Alternative_style_sheets

Support in one engine only.

Firefox3+Safari?Chrome1–48
OperaYesEdgeNo
Edge (Legacy)?Internet Explorer8+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android?

The title attribute on style elements defines CSS 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. If the style element is not in a document tree, then the title attribute is ignored. [CSSOM]

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.

The child text content of a style element must be that of a conformant style sheet.

A style element is implicitly potentially render-blocking if the element was created by its node document's parser.


The user agent must run the update a style block algorithm whenever any of the following conditions occur:

The update a style block algorithm is as follows:

  1. Let element be the style element.

  2. If element has an associated CSS style sheet, remove the CSS style sheet in question.

  3. If element is not connected, then return.

  4. If element's type attribute is present and its value is neither the empty string nor an ASCII case-insensitive match for "text/css", then return.

    In particular, a type value with parameters, such as "text/css; charset=utf-8", will cause this algorithm to return early.

  5. If the Should element's inline behavior be blocked by Content Security Policy? algorithm returns "Blocked" when executed upon the style element, "style", and the style element's child text content, then return. [CSP]

  6. Create a CSS style sheet with the following properties:

    type

    text/css

    owner node

    element

    media

    The media attribute of element.

    This is a reference to the (possibly absent at this time) attribute, rather than a copy of the attribute's current value. CSSOM defines what happens when the attribute is dynamically set, changed, or removed.

    title

    The title attribute of element, if element is in a document tree, or the empty string otherwise.

    Again, this is a reference to the attribute.

    alternate flag

    Unset.

    origin-clean flag

    Set.

    location
    parent CSS style sheet
    owner CSS rule

    null

    disabled flag

    Left at its default value.

    CSS rules

    Left uninitialized.

    This doesn't seem right. Presumably we should be using the element's child text content? Tracked as issue #2997.

  7. If element contributes a script-blocking style sheet, append element to its node document's script-blocking style sheet set.

  8. If element's media attribute's value matches the environment and element is potentially render-blocking, then block rendering on element.

Once the attempts to obtain the style sheet's critical subresources, if any, are complete, or, if the style sheet has no critical subresources, once the style sheet has been parsed and processed, the user agent must run these steps:

Fetching the critical subresources is not well-defined; probably issue #968 is the best resolution for that. In the meantime, any critical subresource request should have its render-blocking set to whether or not the style element is currently render-blocking.

  1. Let element be the style element associated with the style sheet in question.

  2. Let success be true.

  3. If the attempts to obtain any of the style sheet's critical subresources failed for any reason (e.g., DNS error, HTTP 404 response, a connection being prematurely closed, unsupported Content-Type), set success to false.

    Note that content-specific errors, e.g., CSS parse errors or PNG decoding errors, do not affect success.

  4. Queue an element task on the networking task source given element and the following steps:

    1. If success is true, fire an event named load at element.

    2. Otherwise, fire an event named error at element.

    3. If element contributes a script-blocking style sheet:

      1. Assert: element's node document's script-blocking style sheet set contains element.

      2. Remove element from its node document's script-blocking style sheet set.

    4. Unblock rendering on element.

The element must delay the load event of the element's node document until all the attempts to obtain the style sheet's critical subresources, if any, are complete.

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

HTMLStyleElement/media

Support in all current engines.

Firefox1+Safari1+Chrome1+
Opera12.1+Edge79+
Edge (Legacy)12+Internet Explorer5.5+
Firefox Android?Safari iOS?Chrome Android?WebView Android?Samsung Internet?Opera Android12.1+

The media and blocking IDL attributes must each reflect the respective content attributes of the same name.

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

The following document has its stress emphasis styled as bright red text rather than italics text, while leaving titles of works and Latin words in their default italics. It shows how using appropriate elements enables easier restyling of documents.

<!DOCTYPE html>
<html lang="en-US">
 <head>
  <title>My favorite book</title>
  <style>
   body { color: black; background: white; }
   em { font-style: normal; color: red; }
  </style>
 </head>
 <body>
  <p>My <em>favorite</em> book of all time has <em>got</em> to be
  <cite>A Cat's Life</cite>. It is a book by P. Rahmel that talks
  about the <i lang="la">Felis catus</i> in modern human society.</p>
 </body>
</html>

4.2.7 Interactions of styling and scripting

If the style sheet referenced no other resources (e.g., it was an internal style sheet given by a style element with no @import rules), then the style rules must be immediately made available to script; otherwise, the style rules must only be made available to script once the event loop reaches its update the rendering step.

An element el in the context of a Document of an HTML parser or XML parser contributes a script-blocking style sheet if all of the following conditions are true:

It is expected that counterparts to the above rules also apply to <?xml-stylesheet?> PIs. However, this has not yet been thoroughly investigated.

A Document has a script-blocking style sheet set, which is an ordered set, initially empty.

A Document document has a style sheet that is blocking scripts if the following steps return true:

  1. If document's script-blocking style sheet set is not empty, then return true.

  2. If document's node navigable is null, then return false.

  3. Let containerDocument be document's node navigable's container document.

  4. If containerDocument is non-null and containerDocument's script-blocking style sheet set is not empty, then return true.

  5. Return false.

A Document has no style sheet that is blocking scripts if it does not have a style sheet that is blocking scripts.