head
elementhtml
element.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.title
element and no more than one is a base
element.head
element's start tag may be omitted if
the element is empty, or if the first thing inside the head
element is an element.head
element's end tag may be omitted if the
head
element is not immediately followed by a space character or a comment.interface HTMLHeadElement : HTMLElement {};
The head
element represents a collection of metadata for the
Document
.
The collection of metadata in a head
element can be large or small. Here is an
example of a very short one:
<!doctype html> <html> <head> <title>A document with a short head</title> </head> <body> ...
Here is an example of a longer one:
<!DOCTYPE HTML> <HTML> <HEAD> <META CHARSET="UTF-8"> <BASE HREF="http://www.example.com/"> <TITLE>An application with a long head</TITLE> <LINK REL="STYLESHEET" HREF="default.css"> <LINK REL="STYLESHEET ALTERNATE" HREF="big.css" TITLE="Big Text"> <SCRIPT SRC="support.js"></SCRIPT> <META NAME="APPLICATION-NAME" CONTENT="Long headed application"> </HEAD> <BODY> ...
The title
element is a required child in most situations, but when a
higher-level protocol provides title information, e.g. in the Subject line of an e-mail when HTML
is used as an e-mail authoring format, the title
element can be omitted.
title
elementhead
element containing no other title
elements.interface HTMLTitleElement : HTMLElement { attribute DOMString text; };
The title
element represents the document's title or name. Authors
should use titles that identify their documents even when they are used out of context, for
example in a user's history or bookmarks, or in search results. The document's title is often
different from its first heading, since the first heading does not have to stand alone when taken
out of context.
There must be no more than one title
element per document.
If it's reasonable for the Document
to have no title, then the
title
element is probably not required. See the head
element's content
model for a description of when the element is required.
text
[ = value ]Returns the contents of the element, ignoring child nodes that aren't Text
nodes.
Can be set, to replace the element's children with the given value.
The IDL attribute text
must return a
concatenation of the contents of all the Text
nodes that are children of the
title
element (ignoring any other nodes such as comments or elements), in tree order.
On setting, it must act the same way as the textContent
IDL attribute.
Here are some examples of appropriate titles, contrasted with the top-level headings that might be used on those same pages.
<title>Introduction to The Mating Rituals of Bees</title> ... <h1>Introduction</h1> <p>This companion guide to the highly successful <cite>Introduction to Medieval Bee-Keeping</cite> book is...
The next page might be a part of the same site. Note how the title describes the subject matter unambiguously, while the first heading assumes the reader knows what the context is and therefore won't wonder if the dances are Salsa or Waltz:
<title>Dances used during bee mating rituals</title> ... <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.
base
elementhead
element containing no other base
elements.href
— Document base URLtarget
— Default browsing context for hyperlink navigation and form submissioninterface HTMLBaseElement : HTMLElement { attribute DOMString href; attribute DOMString target; };
The base
element allows authors to specify the document base URL for
the purposes of resolving relative URLs, and the name of the
default browsing context for the purposes of following hyperlinks. The
element does not represent any content beyond this
information.
There must be no more than one base
element per document.
A base
element must have either an href
attribute, a target
attribute, or both.
The href
content attribute, if specified, must
contain a valid URL potentially surrounded by spaces.
A base
element, if it has an href
attribute,
must come before any other elements in the tree that have attributes defined as taking URLs, except the html
element (its manifest
attribute isn't affected by base
elements).
The target
attribute, if specified, must
contain a valid browsing context name or keyword, which specifies which
browsing context is to be used as the default when hyperlinks and forms in the
Document
cause navigation.
A base
element, if it has a target
attribute, must come before any elements in the tree that represent hyperlinks.
If there are multiple base
elements with target
attributes, all but the first are ignored.
A base
element that is the first base
element with an href
content attribute in a particular Document
has a
frozen base URL. The frozen base URL must be set, synchronously, whenever any of the following situations occur:
base
element becomes the first base
element in tree
order with an href
content attribute in its
Document
.base
element is the first base
element in tree
order with an href
content attribute in its
Document
, and its href
content attribute is
changed.To set the frozen base URL, resolve
the value of the element's href
content attribute relative to
the Document
's fallback base URL; if this is successful, set the
frozen base URL to the resulting absolute URL, otherwise, set the
frozen base URL to the fallback base URL.
The href
IDL attribute, on getting, must return
the result of running the following algorithm:
If the base
element has no href
content
attribute, then return the document base URL and abort these steps.
Let fallback base url be the Document
's fallback
base URL.
Let url be the value of the href
attribute of the base
element.
Resolve url relative to fallback base url (thus, the base
href
attribute isn't affected by xml:base
attributes or base
elements).
If the previous step was successful, return the resulting absolute URL and abort these steps.
Otherwise, return the empty string.
The href
IDL attribute, on setting, must set the href
content attribute to the given new value.
The target
IDL attribute must
reflect the content attribute of the same name.
In this example, a base
element is used to set the document base
URL:
<!DOCTYPE html> <html> <head> <title>This is an example for the <base> element</title> <base href="http://www.example.com/news/index.html"> </head> <body> <p>Visit the <a href="archives.html">archives</a>.</p> </body> </html>
The link in the above example would be a link to "http://www.example.com/news/archives.html
".
link
elementitemprop
attribute is present: flow content.itemprop
attribute is present: phrasing content.noscript
element that is a child of a head
element.itemprop
attribute is present: where phrasing content is expected.href
— Address of the hyperlinkcrossorigin
— How the element handles crossorigin requestsrel
— Relationship between the document containing the hyperlink and the destination resourcemedia
— Applicable mediahreflang
— Language of the linked resourcetype
— Hint for the type of the referenced resourcesizes
— Sizes of the icons (for rel
="icon
")title
attribute has special semantics on this element: Title of the link; alternative style sheet set name.link
(default - do not set).aria-*
attributes applicable to the allowed roles.role
value interface HTMLLinkElement : HTMLElement {
attribute DOMString href;
attribute DOMString crossOrigin;
attribute DOMString rel;
readonly attribute DOMTokenList relList;
attribute DOMString media;
attribute DOMString hreflang;
attribute DOMString type;
[PutForwards=value] readonly attribute DOMSettableTokenList sizes;
};
HTMLLinkElement implements LinkStyle;
The link
element allows authors to link their document to other resources.
The destination of the link(s) is given by the href
attribute, which must be present and must contain a
valid non-empty URL potentially surrounded by spaces. If the href
attribute is absent, then the element does not define a
link.
A link
element must have either a rel
attribute
or an itemprop
attribute, but not both.
If the rel
attribute is used, the element is
restricted to the head
element. When used with the itemprop
attribute, the element can be used both in the
head
element and in the body
of the page, subject to the constraints of
the microdata model.
The types of link indicated (the relationships) are given by the value of the rel
attribute, which, if present, must have a value that
is a set of space-separated tokens. The allowed keywords and
their meanings are defined in a later section. If the rel
attribute is absent, has no keywords, or if none of the keywords
used are allowed according to the definitions in this specification, then the element does not
create any links.
Two categories of links can be created using the link
element: Links to external resources and hyperlinks. The link types section defines
whether a particular link type is an external resource or a hyperlink. One link
element can create multiple links (of which some might be external resource links and some might
be hyperlinks); exactly which and how many links are created depends on the keywords given in the
rel
attribute. User agents must process the links on a per-link
basis, not a per-element basis.
Each link created for a link
element is handled separately. For
instance, if there are two link
elements with rel="stylesheet"
,
they each count as a separate external resource, and each is affected by its own attributes
independently. Similarly, if a single link
element has a rel
attribute with the value next stylesheet
,
it creates both a hyperlink (for the next
keyword) and
an external resource link (for the stylesheet
keyword), and they are affected by other attributes (such as media
or title
)
differently.
For example, the following link
element creates two hyperlinks (to the same
page):
<link rel="author license" href="/about">
The two links created by this element are one whose semantic is that the target page has information about the current page's author, and one whose semantic is that the target page has information regarding the license under which the current page is provided.
The crossorigin
attribute is a CORS
settings attribute. It is intended for use with external resource links.
The exact behavior for links to external resources depends on the exact relationship, as defined for the relevant link type. Some of the attributes control whether or not the external resource is to be applied (as defined below).
For external resources that are represented in the DOM (for example, style sheets), the DOM representation must be made available (modulo cross-origin restrictions) even if the resource is not applied. To obtain the resource, the user agent must run the following steps:
If the href
attribute's value is the empty string,
then abort these steps.
Resolve the URL given by the href
attribute, relative to the element.
If the previous step fails, then abort these steps.
Do a potentially CORS-enabled fetch of the resulting absolute
URL, with the mode being the current state of the element's crossorigin
content attribute, the origin
being the origin of the link
element's Document
, and the
default origin behaviour set to taint.
The resource obtained in this fashion can be either CORS-same-origin or CORS-cross-origin.
User agents may opt to only try to obtain such resources when they are needed, instead of pro-actively fetching all the external resources that are not applied.
The semantics of the protocol used (e.g. HTTP) must be followed when fetching external resources. (For example, redirects will be followed and 404 responses will cause the external resource to not be applied.)
Once the attempts to obtain the resource and its critical subresources are
complete, the user agent must, if the loads were successful, queue a task to
fire a simple event named load
at the
link
element, or, if the resource or one of its critical subresources
failed to completely load for any reason (e.g. DNS error, HTTP 404 response, a connection being
prematurely closed, unsupported Content-Type), queue a task to fire a simple
event named error
at the link
element.
Non-network errors in processing the resource or its subresources (e.g. CSS parse errors, PNG
decoding errors) are not failures for the purposes of this paragraph.
The task source for these tasks is the DOM manipulation task source.
The element must delay the load event of the element's document until all the attempts to obtain the resource and its critical subresources are complete. (Resources that the user agent has not yet attempted to obtain, e.g. because it is waiting for the resource to be needed, do not delay the load event.)
Interactive user agents may provide users with a means to follow the hyperlinks created using the link
element, somewhere
within their user interface. The exact interface is not defined by this specification, but it
could include the following information (obtained from the element's attributes, again as defined
below), in some form or another (possibly simplified), for each hyperlink created with each
link
element in the document:
rel
attribute)title
attribute).href
attribute).hreflang
attribute).media
attribute).User agents could also include other information, such as the type of the resource (as given by
the type
attribute).
Hyperlinks created with the link
element and its rel
attribute apply to the whole page. This contrasts with the rel
attribute of a
and area
elements,
which indicates the type of a link whose context is given by the link's location within the
document.
The media
attribute says which media the
resource applies to. The value must be a valid media query.
If the link is a hyperlink then the media
attribute is purely advisory, and describes for which media the document in question was
designed.
However, if the link is an external resource link, then the media
attribute is prescriptive. The user agent must apply the
external resource when the media
attribute's value
matches the environment and the other relevant conditions apply, and must not apply
it otherwise.
The external resource might have further restrictions defined within that limit
its applicability. For example, a CSS style sheet might have some @media
blocks. This specification does not override such further restrictions or requirements.
The default, if the media
attribute is
omitted, is "all
", meaning that by default links apply to all media.
The hreflang
attribute on the
link
element has the same semantics as the hreflang
attribute on a
and
area
elements.
The type
attribute gives the MIME
type of the linked resource. It is purely advisory. The value must be a valid MIME
type.
For external resource links, the type
attribute is used as a hint to user agents so that they can
avoid fetching resources they do not support. If the attribute is present, then
the user agent must assume that the resource is of the given type (even if that is not a
valid MIME type, e.g. the empty string). If the attribute is omitted, but the
external resource link type has a default type defined, then the user agent must assume that the
resource is of that type. If the UA does not support the given MIME type for the
given link relationship, then the UA should not obtain
the resource; if the UA does support the given MIME type for the given link
relationship, then the UA should obtain the resource at
the appropriate time as specified for the external resource link's particular type.
If the attribute is omitted, and the external resource link type does not have a default type
defined, but the user agent would obtain the resource if
the type was known and supported, then the user agent should obtain the resource under the assumption that it will be
supported.
User agents must not consider the type
attribute
authoritative — upon fetching the resource, user agents must not use the type
attribute to determine its actual type. Only the actual type
(as defined in the next paragraph) is used to determine whether to apply the resource,
not the aforementioned assumed type.
If the external resource link type defines rules for processing the resource's Content-Type metadata, then those rules apply. Otherwise, if the resource is expected to be an image, user agents may apply the image sniffing rules, with the official type being the type determined from the resource's Content-Type metadata, and use the resulting sniffed type of the resource as if it was the actual type. Otherwise, if neither of these conditions apply or if the user agent opts not to apply the image sniffing rules, then the user agent must use the resource's Content-Type metadata to determine the type of the resource. If there is no type metadata, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type.
The stylesheet
link type defines rules for
processing the resource's Content-Type metadata.
Once the user agent has established the type of the resource, the user agent must apply the resource if it is of a supported type and the other relevant conditions apply, and must ignore the resource otherwise.
If a document contains style sheet links labeled as follows:
<link rel="stylesheet" href="A" type="text/plain"> <link rel="stylesheet" href="B" type="text/css"> <link rel="stylesheet" href="C">
...then a compliant 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 title
attribute gives the title of the
link. With one exception, it is purely advisory. The value is text. The exception is for style
sheet links, where the title
attribute defines
alternative style sheet sets.
The title
attribute on link
elements differs from the global title
attribute of most other
elements in that a link without a title does not inherit the title of the parent element: it
merely has no title.
The sizes
attribute is used with the icon
link type. The attribute must not be specified on link
elements that do not have a rel
attribute that specifies the
icon
keyword.
The activation behavior of link
elements that create hyperlinks is to run the following steps:
If the link
element's Document
is not fully active,
then abort these steps.
Follow the hyperlink created by the
link
element.
HTTP Link:
headers, if supported, must be assumed to come before
any links in the document, in the order that they were given in the HTTP message. These headers
are to be processed according to the rules given in the relevant specifications. [HTTP] [WEBLINK]
Registration of relation types in HTTP Link: headers is distinct from HTML link types, and thus their semantics can be different from same-named HTML types.
The IDL attributes href
, rel
, media
,
hreflang
, type
, and sizes
each must reflect the respective
content attributes of the same name.
The crossOrigin
IDL attribute must
reflect the crossorigin
content attribute,
limited to only known values.
The IDL attribute relList
must reflect the rel
content attribute.
The LinkStyle
interface is also implemented by this element. [CSSOM]
Here, a set of link
elements provide some style sheets:
<!-- a persistent style sheet --> <link rel="stylesheet" href="default.css"> <!-- the preferred alternate style sheet --> <link rel="stylesheet" href="green.css" title="Green styles"> <!-- some alternate style sheets --> <link rel="alternate stylesheet" href="contrast.css" title="High contrast"> <link rel="alternate stylesheet" href="big.css" title="Big fonts"> <link rel="alternate stylesheet" href="wide.css" title="Wide screen">
The following example shows how you can specify versions of the page that use alternative formats, are aimed at other languages, and that are intended for other media:
<link rel=alternate href="/en/html" hreflang=en type=text/html title="English HTML"> <link rel=alternate href="/fr/html" hreflang=fr type=text/html title="French HTML"> <link rel=alternate href="/en/html/print" hreflang=en type=text/html media=print title="English HTML (for printing)"> <link rel=alternate href="/fr/html/print" hreflang=fr type=text/html media=print title="French HTML (for printing)"> <link rel=alternate href="/en/pdf" hreflang=en type=application/pdf title="English PDF"> <link rel=alternate href="/fr/pdf" hreflang=fr type=application/pdf title="French PDF">
meta
elementitemprop
attribute is present: flow content.itemprop
attribute is present: phrasing content.charset
attribute is present, or if the element's http-equiv
attribute is in the Encoding declaration state: in a head
element.http-equiv
attribute is present but not in the Encoding declaration state: in a head
element.http-equiv
attribute is present but not in the Encoding declaration state: in a noscript
element that is a child of a head
element.name
attribute is present: where metadata content is expected.itemprop
attribute is present: where metadata content is expected.itemprop
attribute is present: where phrasing content is expected.name
— Metadata namehttp-equiv
— Pragma directivecontent
— Value of the elementcharset
— Character encoding declarationinterface HTMLMetaElement : HTMLElement { attribute DOMString name; attribute DOMString httpEquiv; attribute DOMString content; };
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 in an XML document, its value must be an
ASCII case-insensitive match for the string "UTF-8
" (and the
document is therefore forced to use UTF-8 as its encoding).
The charset
attribute on the
meta
element has no effect in XML documents, and is only allowed in order to
facilitate migration to and from XHTML.
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 name
and content
IDL attributes must reflect the
respective content attributes of the same name. The IDL attribute httpEquiv
must reflect the content
attribute http-equiv
.
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 attribute to specify the language of each name.
There must not be more than one meta
element with a given language
and with its name
attribute set to the value 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:
Let languages be the list of languages.
Let default language be the language of the
Document
's root element,
if any, and if that language is not unknown.
If there is a default language, and if it is not the same language as any of the languages is languages, append it to languages.
Let winning language be the first language in languages for which there is a meta
element in the
Document
that has its name
attribute set to
the value application-name
and whose
language is the language in question.
If none of the languages have such a meta
element, then abort these steps;
there's no given application name.
Return the value of the content
attribute of the
first meta
element in the Document
in tree order that
has its name
attribute set to the value application-name
and whose language is winning language.
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 with its name
attribute set to
the value 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> <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:
Let keywords be an empty list.
For each meta
element with a name
attribute and a content
attribute and whose name
attribute's value is keywords
, run the following substeps:
Split the value of the element's content
attribute on commas.
Add the resulting tokens, if any, to keywords.
Remove any duplicates from keywords.
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.
Extensions to the predefined set of metadata names may be registered in the WHATWG Wiki MetaExtensions page. [WHATWGWIKI]
Anyone is free to edit the WHATWG Wiki MetaExtensions page at any time to add a type. These new names must be specified with the following information:
The actual name being defined. The name should not be confusingly similar to any other defined name (e.g. differing only in case).
A short non-normative description of what the metadata name's meaning is, including the format the value is required to be in.
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.
One of the following:
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 registered in the "proposed" state for a period of a month or more without being used or specified, then it may be removed from the registry.
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.
Conformance checkers may use the information given on the WHATWG Wiki MetaExtensions page to establish if a value is allowed or not: values defined in this specification or marked as "proposed" or "ratified" must be accepted, whereas values marked as "discontinued" or not listed in either this specification or on the aforementioned page must be reported as invalid. Conformance checkers may cache this information (e.g. for performance reasons or to avoid the use of unreliable network connectivity).
When an author uses a new metadata name not defined by either this specification or the Wiki page, conformance checkers should offer to add the value to the Wiki, with the details described above, with the "proposed" status.
Metadata names whose values are to be URLs must not be proposed or
accepted. Links must be represented using the link
element, not the meta
element.
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.
State | Keyword | Notes |
---|---|---|
Content Language | content-language
| Non-conforming |
Encoding declaration | content-type
| |
Default style | default-style
| |
Refresh | refresh
| |
Cookie setter | set-cookie
| Non-conforming |
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:
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.
If the meta
element has no content
attribute, then abort these steps.
If the element's content
attribute contains a
"," (U+002C) character then abort these steps.
Let input be the value of the element's content
attribute.
Let position point at the first character of input.
Collect a sequence of characters that are not space characters.
Let candidate be the string that resulted from the previous step.
If candidate is the empty string, abort these steps.
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]
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 space characters, followed by the literal string "charset=
", followed by one of the labels of
the character encoding of the character encoding
declaration.
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 and in XML Documents. If the
encoding declaration state is used in
XML Documents, the name of the character
encoding must be an ASCII case-insensitive match for the string "UTF-8
" (and the document is therefore forced to use UTF-8 as its encoding).
The encoding declaration state has no effect in XML documents, and is only allowed in order to facilitate migration to and from XHTML.
http-equiv="default-style"
)
This pragma sets the name of the default alternative style sheet set.
If the meta
element has no content
attribute, or if that attribute's value is the empty string, then abort these steps.
Set the preferred style sheet set to the value of the element's content
attribute. [CSSOM]
http-equiv="refresh"
)
This pragma acts as timed redirect.
If another meta
element with an http-equiv
attribute in the Refresh state has already been successfully
processed (i.e. when it was inserted the user agent processed it and reached the last step of
this list of steps), then abort these steps.
If the meta
element has no content
attribute, or if that attribute's value is the empty string, then abort these steps.
Let input be the value of the element's content
attribute.
Let position point at the first character of input.
Collect a sequence of characters that are ASCII digits, and parse the resulting string using the rules for parsing non-negative integers. If the sequence of characters collected is the empty string, then no number will have been parsed; abort these steps. Otherwise, let time be the parsed number.
Collect a sequence of characters that are ASCII digits and "." (U+002E) characters. Ignore any collected characters.
Let url be the address of the current page.
If the character in input pointed to by position is a ";" (U+003B) character or a "," (U+002C) character, then advance position to the next character. Otherwise, jump to the last step.
If the character in input pointed to by position is a "U" (U+0055) character or a U+0075 LATIN SMALL LETTER U character (u), then advance position to the next character. Otherwise, jump to the last step.
If the character in input pointed to by position is a "R" (U+0052) character or a U+0072 LATIN SMALL LETTER R character (r), then advance position to the next character. Otherwise, jump to the last step.
If the character in input pointed to by position is s "L" (U+004C) character or a U+006C LATIN SMALL LETTER L character (l), then advance position to the next character. Otherwise, jump to the last step.
If the character in input pointed to by position is a "=" (U+003D), then advance position to the next character. Otherwise, jump to the last step.
If the character in input pointed to by position is either a "'" (U+0027) character or """ (U+0022) character, then let quote be that character, and advance position to the next character. Otherwise, let quote be the empty string.
Let url be equal to the substring of input from the character at position to the end of the string.
If quote is not the empty string, and there is a character in url equal to quote, then truncate url at that character, so that it and all subsequent characters are removed.
Strip any trailing space characters from the end of url.
Strip any "tab" (U+0009), "LF" (U+000A), and "CR" (U+000D) characters from url.
Resolve the url value to an
absolute URL, relative to the meta
element. If this fails, abort
these steps.
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 the meta
element's Document
's active
sandboxing flag set does not have the sandboxed automatic features browsing
context flag set, navigate the
Document
's browsing context to url, with
replacement enabled, and with the Document
's browsing
context as the source browsing context.
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:
meta
element was inserted into the
Document
, adjusted to take into account user or user agent
preferences.Provide the user with an interface that, when selected, navigates a browsing context to
url, with the Document
's browsing context as
the source browsing context.
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:
URL
", followed by a "=" (U+003D) character, followed by a valid
URL that does not start with a literal "'" (U+0027) or """ (U+0022) character.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">
http-equiv="set-cookie"
)
This pragma sets an HTTP cookie. [COOKIES]
It is non-conforming. Real HTTP headers should be used instead.
If the meta
element has no content
attribute, or if that attribute's value is the empty string, then abort these steps.
Act as if receiving a
set-cookie-string for the document's address via a "non-HTTP" API,
consisting of the value of the element's content
attribute encoded as UTF-8. [COOKIES] [ENCODING]
There must not be more than one meta
element with any particular state in the
document at a time.
Extensions to the predefined set of pragma directives may, under certain conditions, be registered in the WHATWG Wiki PragmaExtensions page. [WHATWGWIKI]
Such extensions must use a name that is identical to an HTTP header registered in the Permanent Message Header Field Registry, and must have behavior identical to that described for the HTTP header. [IANAPERMHEADERS]
Pragma directives corresponding to headers describing metadata, or not requiring specific user agent processing, must not be registered; instead, use metadata names. Pragma directives corresponding to headers that affect the HTTP processing model (e.g. caching) must not be registered, as they would result in HTTP-level behavior being different for user agents that implement HTML than for user agents that do not.
Anyone is free to edit the WHATWG Wiki PragmaExtensions page at any time to add a pragma directive satisfying these conditions. Such registrations must specify the following information:
The actual name being defined. The name must match a previously-registered HTTP name with the same requirements.
A short non-normative description of the purpose of the pragma directive.
Conformance checkers must use the information given on the WHATWG Wiki PragmaExtensions page to establish if a value is allowed or not: values defined in this specification or listed on the aforementioned page must be accepted, whereas values not listed in either this specification or on the aforementioned page must be rejected as invalid. Conformance checkers may cache this information (e.g. for performance reasons or to avoid the use of unreliable network connectivity).
A character encoding declaration is a mechanism by which the character encoding used to store or transmit a document is specified.
The following restrictions apply to character encoding declarations:
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 character encoding used must be
an ASCII-compatible character encoding, and 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 if the encoding is US-ASCII, 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.
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
.)
If an HTML document contains a meta
element
with a charset
attribute or a meta
element
with an http-equiv
attribute in the Encoding declaration state, then the character
encoding used must be an ASCII-compatible character encoding.
Authors should use UTF-8. Conformance checkers may advise authors against using legacy encodings. [ENCODING]
Authoring tools should default to using UTF-8 for newly-created documents. [ENCODING]
Encodings in which a series of bytes in the range 0x20 to 0x7E can encode characters other than
the corresponding characters in the range U+0020 to U+007E represent a potential security
vulnerability: a user agent that does not support the encoding (or does not support the label used
to declare the encoding, or does not use the same mechanism to detect the encoding of unlabeled
content as another user agent) might end up interpreting technically benign plain text content as
HTML tags and JavaScript. Authors should therefore not use these encodings. For example, this
applies to encodings in which the bytes corresponding to "<script>
" in
ASCII can encode a different string. Authors should not use such encodings, which are known to
include JIS_C6226-1983, JIS_X0212-1990,
HZ-GB-2312, JOHAB (Windows code page 1361), encodings based on
ISO-2022, and encodings
based on EBCDIC. Furthermore, authors must not use the CESU-8, UTF-7, BOCU-1 and SCSU encodings,
which also fall into this category; these encodings were never intended for use for Web content.
[RFC1345]
[RFC1842]
[RFC1468]
[RFC2237]
[RFC1554]
[CP50220]
[RFC1922]
[RFC1557]
[CESU8]
[UTF7]
[BOCU1]
[SCSU]
Authors should not use UTF-32, as the encoding detection algorithms described in this specification intentionally do not distinguish it from UTF-16. [UNICODE]
Using non-UTF-8 encodings can have unexpected results on form submission and URL encodings, which use the document's character encoding by default.
In XHTML, 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"?>
style
elementscoped
attribute is present: flow content.scoped
attribute is absent: where metadata content is expected.scoped
attribute is absent: in a noscript
element that is a child of a head
element.scoped
attribute is present: where flow content is expected, but before any other flow content other than inter-element whitespace and style
elements, and not as the child of an element whose content model is transparent.type
attribute, but must match requirements described in prose below.media
— Applicable mediatype
— Type of embedded resourcescoped
— Whether the styles apply to the entire document or just the parent subtreetitle
attribute has special semantics on this element: Alternative style sheet set name.interface HTMLStyleElement : HTMLElement { attribute DOMString media; attribute DOMString type; attribute boolean scoped; }; HTMLStyleElement implements LinkStyle;
The style
element allows authors to embed style information 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.
The type
attribute gives the styling language.
If the attribute is present, its value must be a valid MIME type that designates a
styling language. The charset
parameter must not be specified. The default
value for the type
attribute, which is used if the attribute
is absent, is "text/css
". [RFC2318]
When examining types to
determine if they support the language, user agents must not ignore unknown MIME parameters
— types with unknown parameters must be assumed to be unsupported. The charset
parameter must be treated as an unknown parameter for the purpose of
comparing MIME types here.
The media
attribute says which media the
styles apply to. The value must be a valid media query. 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 scoped
attribute is a boolean
attribute. If present, it indicates that the styles are intended just for the subtree
rooted at the style
element's parent element, as opposed to the whole
Document
.
If the scoped
attribute is present and the element has a
parent element, then the style
element must precede any flow content in
its parent element other than inter-element whitespace and other style
elements, and the parent element's content model must not have a transparent
component.
This implies that scoped style
elements cannot be children of, e.g.,
a
or ins
elements, even when those are used as flow content
containers.
A style
element without a scoped
attribute is restricted to appearing in the
head
of the document.
A style sheet declared by a style
element that has a scoped
attribute and has a parent node that is an element is
scoped, with the scoping element being the style
element's parent
element. [CSSSCOPED]
The title
attribute on
style
elements defines alternative 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. [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 textContent
of a style
element must match the style
production in the following ABNF, the character set for which is Unicode. [ABNF]
style = no-c-start *( c-start no-c-end c-end no-c-start ) no-c-start = < any string that doesn't contain a substring that matches c-start > c-start = "<!--" no-c-end = < any string that doesn't contain a substring that matches c-end > c-end = "-->"
Whenever one of the following conditions occur:
...the user agent must queue a task to invoke the update a style
block algorithm that applies for the style sheet language specified by the element's type
attribute, passing it the element's style
data.
For styling languages that consist of pure text (as opposed to XML), a style
element's style data is the concatenation of the contents of all the
Text
nodes that are children of the style
element (not any other nodes
such as comments or elements), in tree order. For XML-based styling languages, the
style data consists of all the child nodes of the style
element.
The update a style
block algorithm for CSS (text/css
) is
as follows:
Let element be the style
element.
If element has an associated CSS style sheet, remove the CSS style sheet in question.
If element is not in a Document
, then abort
these steps.
Create a CSS style sheet with the following properties:
text/css
element
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. The CSSOM specification defines what happens when the attribute is dynamically set, changed, or removed.
The title
attribute of element.
Again, this is a reference to the attribute.
Unset.
Set.
null
Left at its default value.
Left uninitialized.
This specification does not define any other styling language's update a style
block algorithm.
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, if the loads were successful or there were
none, queue a task to fire a simple event named load
at the style
element, or, if one of the style sheet's
critical subresources failed to completely load for any reason (e.g. DNS error, HTTP
404 response, a connection being prematurely closed, unsupported Content-Type), queue a
task to fire a simple event named error
at
the style
element. Non-network errors in processing the style sheet or its
subresources (e.g. CSS parse errors, PNG decoding errors) are not failures for the purposes of
this paragraph.
The task source for these tasks is the DOM manipulation task source.
The element must delay the load event of the element's 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]
The media
, type
and scoped
IDL attributes must 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>
@global
ruleThe following will eventually be moved to a CSS specification; it is specified here only on an interim basis until an editor can be found to own this.
Within scoped CSS resources, authors may use an @global
@-rule. The
syntax of this rule is defined as follows.
The following production is added to the grammar:
global : GLOBAL_SYM S* ruleset ;
The following rules are added to the Flex tokenizer:
B b|\\0{0,4}(42|62)(\r\n|[ \t\r\n\f])? @{G}{L}{O}{B}{A}{L} {return GLOBAL_SYM;}
Simple selectors in rule sets prefixed by the @global
@-rule in scoped
CSS resources must be processed in the same way as normal rule sets in non-scoped CSS
resources.
Simple selectors in scoped CSS resources that are not prefixed by an @global
@-rule must only match the style
element's parent element (if
any), and that element's descendants.
Style sheets, whether added by a link
element, a style
element, an
<?xml-stylesheet>
PI, an HTTP Link:
header, or some
other mechanism, have a style sheet ready flag, which is initially unset.
When a style sheet is ready to be applied, its style sheet ready flag must be set.
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 synchronously 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.
A style sheet in the context of the Document
of an HTML parser or
XML parser is said to be a style sheet that is blocking scripts if the
element was created by that Document
's parser, and the element is either a
style
element or a link
element that was an external resource link that contributes to the styling processing
model when the element was created by the parser, and the element's style sheet was enabled
when the element was created by the parser, and the element's style sheet ready flag
is not yet set, and, the last time the event loop reached step 1, the element was
in that Document
, and the user agent hasn't given
up on that particular style sheet yet. A user agent may give up on 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). Implementors 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.
A Document
has a style sheet that is blocking scripts if there is
either a style sheet that is blocking scripts in the context of that
Document
, or if that Document
is in a browsing context that
has a parent browsing context, and the active document of that
parent browsing context itself has a style sheet that is blocking
scripts.
A Document
has no style sheet that is blocking scripts if it does not
have a style sheet that is blocking
scripts as defined in the previous paragraph.