Tóm Tắt

HTML

Living Standard — Last Updated

The elements of HTML

4.1

The document element

4.1.1

The html element

Element/html

Support in all current engines.

Firefox

Yes

Safari

Yes

Chrome

Yes

Opera

Edge

Yes

Edge (Legacy)

12+

Internet Explorer

Yes

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

HTMLHtmlElement

Support in all current engines.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

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.

Firefox

Safari

Yes

Chrome

Opera

Yes

Edge

79+

Edge (Legacy)

12+

Internet Explorer

Yes

Firefox Android

Safari iOS

Chrome Android

Yes

WebView Android

Samsung Internet

Opera Android

HTMLHeadElement

Support in all current engines.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

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.

Firefox

Safari

Chrome

Opera

Yes

Edge

79+

Edge (Legacy)

12+

Internet Explorer

Firefox Android

Safari iOS

Yes

Chrome Android

Yes

WebView Android

Samsung Internet

Opera Android

HTMLTitleElement

Support in all current engines.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

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.

Firefox

Safari

Yes

Chrome

Yes

Opera

Edge

Yes

Edge (Legacy)

12+

Internet Explorer

Yes

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

HTMLBaseElement

Support in all current engines.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

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 . 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, run these steps:

If element has a target attribute, then return that
attribute’s value.
If element’s node document contains a base element
with a target attribute, then return the value of the
target attribute of the first such base
element.
Return the empty string.

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:

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 for an element element:

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

Let document be element’s node document.
Let url be the value of the href
attribute of this element, if it has one, and the empty string otherwise.
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.)
If urlRecord is failure, return url.
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“.

4.2.4

The link element

Element/link

Support in all current engines.

Firefox

Safari

Yes

Chrome

Opera

Yes

Edge

79+

Edge (Legacy)

12+

Internet Explorer

Yes

Firefox Android

Safari iOS

Chrome Android

Yes

WebView Android

Samsung Internet

Opera Android

HTMLLinkElement

Support in all current engines.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

37+

Samsung Internet

Opera Android

12.1+

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,
prerender,
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.

Firefox

43+

Safari

11.1+

Chrome

45+

Opera

Edge

79+

Edge (Legacy)

17+

Internet Explorer

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
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 types modulepreload, preload and
stylesheet, and it must only be specified on link elements
that have a rel attribute containing one of those
keywords.

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/rel

Support in all current engines.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

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.

Firefox

56+

Safari

10+

Chrome

50+

Opera

Edge

79+

Edge (Legacy)

17+

Internet Explorer

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.

Firefox

50+

Safari

14.1+

Chrome

58+

Opera

Edge

79+

Edge (Legacy)

Internet Explorer

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 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.

Firefox

30+

Safari

Chrome

50+

Opera

Edge

79+

Edge (Legacy)

17+

Internet Explorer

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.

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 computed 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 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.

4.2.4.3

Fetching and processing a resource
from a link element

All external resource
links have a fetch and process the linked resource algorithm, which takes a
link element el. They also have linked resource fetch setup
steps which take a link element el and request request. Individual link types may provide
their own fetch and process the linked resource algorithm, but unless explicitly
stated, they use the default fetch and process the linked resource algorithm.
Similarly, individual link types may provide their own linked resource fetch setup
steps, but unless explicitly stated, these steps just return true.

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

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

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.)

4.2.4.4

Processing `Link` headers

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.

The processing of `Link` headers is not defined for
all link relation types. In particular some implementations might process types that have a no-op
process link headers algorithm, and in doing so influence a Document‘s
script-blocking style sheet counter. See
issue #4224 for discussion on
integrating this into the spec.

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

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:

To given a header
list headers:

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

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

4.2.4.5

Early hints

Status/103

Support in one engine only.

Firefox

Safari

Chrome

103+

Opera

Edge

103+

Edge (Legacy)

Internet Explorer

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 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.

Interactive user agents may provide users with a means to created using the 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 created
with each element in the document:

The relationship between this document and the resource (given by the attribute)
The title of the resource (given by the
attribute).
The address of the resource (given by the
attribute).
The language of the resource (given by the
attribute).
The optimum media for the resource (given by the
attribute).

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

4.2.5

The
element

Element/meta

Support in all current engines.

Firefox

Safari

Yes

Chrome

Yes

Opera

Edge

Yes

Edge (Legacy)

12+

Internet Explorer

Yes

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

HTMLMetaElement

Support in all current engines.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

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.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

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.

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:

If either the name is a URL, or the value of its accompanying content attribute is a URL; in those cases,
registering it as an extension to the predefined set of
link types is encouraged (rather than creating a new metadata name).
If the name is for something expected to have processing requirements in user agents; in
that case it ought to be standardized.

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. The following table lists the keywords defined for this attribute. The states
given in the first cell of the rows with keywords give the states to which those keywords map.
Some of the keywords are non-conforming, as noted in the last
column.

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:

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:

The character encoding declaration must be serialized without the use of character references or character escapes of any kind.
The element containing the character encoding
declaration must be serialized completely within the first 1024 bytes of the
document.

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.

Firefox

Safari

Chrome

Opera

3.5+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

10.1+

HTMLStyleElement

Support in all current engines.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

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.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

13+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

The disabled getter steps are:

The disabled setter steps are:

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.

Firefox

Safari

Chrome

1–48

Opera

Yes

Edge

Edge (Legacy)

Internet Explorer

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 algorithm whenever
one of the following conditions occur:

The algorithm is as follows:

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.

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.

Firefox

Safari

Chrome

Opera

12.1+

Edge

79+

Edge (Legacy)

12+

Internet Explorer

5.5+

Firefox Android

Safari iOS

Chrome Android

WebView Android

Samsung Internet

Opera Android

12.1+

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

The 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 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:

el was created by that Document‘s parser.
el is either a style element or a link element that
was an external resource link that contributes to the styling
processing model when the el was created by the parser.
el’s media attribute’s value
matches the environment.
el’s style sheet was enabled when the element was created by the
parser.
The last time the event loop reached step 1,
el’s root was that Document.
The user agent hasn’t given up on loading that particular style sheet yet. A user agent
may give up on loading a style sheet at any time.

Giving up on a style sheet before the style sheet loads, if the style sheet
eventually does still load, means that the script might end up operating with incorrect
information. For example, if a style sheet sets the color of an element to green, but a script
that inspects the resulting style is executed before the sheet is loaded, the script will find
that the element is black (or whatever the default color is), and might thus make poor choices
(e.g., deciding to use black as the color elsewhere on the page, instead of green). Implementers
have to balance the likelihood of a script using incorrect information with the performance impact
of doing nothing while waiting for a slow network request to finish.

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

A Document has a script-blocking style sheet counter, which is a
number, initially 0.

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

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

HTML Standard

HTML

Living Standard — Last Updated

mtoplist