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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang=en>
<head profile="http://dublincore.org/documents/2008/08/04/dc-html/ ">
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Namespaces Module</title>
<link href="http://purl.org/dc/terms/" rel=schema.dcterms>
<link href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=dcterms.rights>
<meta content="CSS Namespaces Module" name=dcterms.title>
<meta content=text name=dcterms.type>
<meta content=2013-06-08 name=dcterms.date>
<meta content="Elika J. Etemad" name=dcterms.creator>
<meta content="Anne van Kesteren" name=dcterms.creator>
<meta content=W3C name=dcterms.publisher>
<meta content="http://dev.w3.org/csswg/css3-namespace/"
name=dcterms.identifier>
<link href="../default.css" rel=stylesheet type="text/css">
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED" rel=stylesheet
type="text/css">
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1>CSS Namespaces Module</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 8 June 2013</h2>
<dl>
<dt>This version:</dt>
<!--
<dd><a href="http://dev.w3.org/csswg/css3-namespace/">http://www.w3.org/TR/2013/PR-css3-namespace-20130608/</a></dd>
-->
<dd><a
href="http://dev.w3.org/csswg/css3-namespace/">http://dev.w3.org/csswg/css3-namespace/</a>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-namespace/">http://www.w3.org/TR/css3-namespace/</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2008/CR-css3-namespace-20080523/">http://www.w3.org/TR/2008/CR-css3-namespace-20080523/</a>
<dt>Feedback:
<dd><a
href="mailto:www-style@w3.org?subject=%5Bcss-namespaces%5D%20feedback">www-style@w3.org</a>
with subject line “<kbd>[css-namespaces] <var>… message topic
…</var></kbd>” (<a
href="http://lists.w3.org/Archives/Public/www-style/"
rel=discussion>archives</a>)
<dt>Editors:
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a>
<dd><a href="http://annevankesteren.nl/about">Anne van Kesteren</a>,
Opera Software ASA
<dt>Previous Editors:
<dd>Peter Linss, Netscape Communications
<dd>Chris Lilley, W3C
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2013 <a href="http://www.w3.org/"><abbr
title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><abbr
title="Massachusetts Institute of Technology">MIT</abbr></a>, <a
href="http://www.ercim.eu/"><abbr
title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>, <a
href="http://ev.buaa.edu.cn/">Beihang</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p>This CSS Namespaces module defines the syntax for using namespaces in
CSS. It defines the <code>@namespace</code> rule for declaring the default
namespace and binding namespaces to namespace prefixes, and it also
defines a syntax that other specifications can adopt for using those
prefixes in namespace-qualified names.
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<!--begin-status-->
<p>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. Its publication here does
not imply endorsement of its contents by W3C. Don't cite this document
other than as work in progress.
<p>The (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a
href="mailto:www-style@w3.org?Subject=%5Bcss3-namespace%5D%20PUT%20SUBJECT%20HERE">
www-style@w3.org</a> (see <a
href="http://www.w3.org/Mail/Request">instructions</a>) is preferred for
discussion of this specification. When sending e-mail, please put the text
“css3-namespace” in the subject, preferably like this:
“[<!---->css3-namespace<!---->] <em>…summary of comment…</em>”
<p>This document was produced by the <a
href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of
the <a href="http://www.w3.org/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
2004 W3C Patent Policy</a>. W3C maintains a <a
href="http://www.w3.org/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
6 of the W3C Patent Policy</a>.</p>
<!--end-status-->
<p>A CSS Namespace <a href="http://www.w3.org/Style/CSS/Test/">Test
Suite</a> has been developed during the Candidate Recommendation phase of
this CSS Namespaces specification. An <a
href="/Style/CSS/Test/CSS3/Namespace/20090210/reports/implement-report.html">implementation
report</a> is also available.
<p>This document is the same as the previous, Candidate Recommendation
version, except for editorial changes.
<p><em>W3C asks that members of the W3C Advisory Committee review this
document and fill in the corresponding <a
href="/2002/09/wbs/33280/PR-css3-namespace/">online form
[member-only].</a> The review closes on 8 September 2011.</em>
<h2 class="no-num no-toc" id=contents>Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#intro"><span class=secno>1. </span>Introduction</a>
<li><a href="#conformance"><span class=secno>2. </span>Conformance</a>
<ul class=toc>
<li><a href="#terminology"><span class=secno>2.1. </span>Terminology</a>
</ul>
<li><a href="#declaration"><span class=secno>3. </span>Declaring
namespaces: the <code>@namespace</code> rule</a>
<ul class=toc>
<li><a href="#syntax"><span class=secno>3.1. </span>Syntax</a>
<li><a href="#scope"><span class=secno>3.2. </span>Scope</a>
<li><a href="#prefixes"><span class=secno>3.3. </span>Declaring
Prefixes</a>
</ul>
<li><a href="#css-qnames"><span class=secno>4. </span>CSS Qualified
Names</a>
<li class=no-num><a href="#acknowledgments">Acknowledgments</a>
<li class=no-num><a href="#references">References</a>
<ul class=toc>
<li class=no-num><a href="#normative-references">Normative
references</a>
<li class=no-num><a href="#informative-references">Informative
references</a>
</ul>
</ul>
<!--end-toc-->
<div>
<h2 id=intro><span class=secno>1. </span>Introduction</h2>
<p><em>This section is non-normative.</em>
<p>This CSS Namespaces module defines syntax for using namespaces in CSS.
It defines the <code>@namespace</code> rule for declaring a default
namespace and for binding namespaces to namespace prefixes. It also
defines a syntax for using those prefixes to represent
namespace-qualified names. It does not define where such names are valid
or what they mean: that depends on their context and is defined by a host
language, such as Selectors (<a href="#SELECT"
rel=biblioentry>[SELECT]<!--{{SELECT}}--></a>), that references the
syntax defined in the CSS Namespaces module.
<p>Note that a CSS client that does not support this module will (if it
properly conforms to <a
href="http://www.w3.org/TR/CSS21/syndata.html#parsing-errors">CSS's
forward-compatible parsing rules</a>) ignore all <code>@namespace</code>
rules, as well as all style rules that make use of namespace qualified
names. The syntax of delimiting namespace prefixes in CSS was
deliberately chosen so that these CSS clients would ignore the style
rules rather than possibly match them incorrectly.
</div>
<div>
<h2 id=conformance><span class=secno>2. </span>Conformance</h2>
<p>A document or implementation cannot conform to CSS Namespaces alone,
but can claim conformance to CSS Namespaces if it satisfies the
conformance requirements in this specification when implementing CSS or
another host language that normatively references this specification.
<p>Conformance to CSS Namespaces is defined for two classes:
<dl>
<dt><dfn id=style-sheet>style sheet</dfn>
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
style sheet</a> (or a complete unit of another host language that
normatively references CSS Namespaces).
<dt><dfn id=interpreter>interpreter</dfn>
<dd>Someone or something that interprets the semantics of a style sheet.
(CSS <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">user
agents</a> fall under this category.)
</dl>
<p>The conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this
document are to be interpreted as described in RFC 2119. However, for
readability, these words do not appear in all uppercase letters in this
specification. All of the text of this specification is normative except
sections explicitly marked as non-normative, examples, and notes. <a
href="#RFC2119" rel=biblioentry>[RFC2119]<!--{{!RFC2119}}--></a>
<p>Examples in this specification are introduced with the words "for
example" or are set apart from the normative text with
<code>class="example"</code>, like this:
<div class=example>
<p>This is an example of an informative example.
</div>
<p>Informative notes begin with the word "Note" and are set apart from the
normative text with <code>class="note"</code>, like this:
<p class=note>Note, this is an informative note.
<h3 id=terminology><span class=secno>2.1. </span>Terminology</h3>
<p>Besides terms introduced by this specification, CSS Namespaces uses the
terminology defined in Namespaces in XML 1.0. <a href="#XML-NAMES"
rel=biblioentry>[XML-NAMES]<!--{{!XML-NAMES}}--></a> However, the syntax
defined here is not restricted to representing XML element and attribute
names and may represent other kinds of namespaces as defined by the host
language.
<p>In CSS Namespaces a namespace name consisting of the empty string is
taken to represent the null namespace or lack of a namespace.
<div class=example>
<p>For example, given the namespace declarations:
<pre>@namespace empty "";
<!-- -->@namespace "";</pre>
<p>The <a href="http://www.w3.org/TR/css3-selectors/#type-selectors">type
selectors</a> <code>elem</code>, <code>|elem</code>, and
<code>empty|elem</code> are equivalent.
</div>
</div>
<div>
<h2 id=declaration><span class=secno>3. </span>Declaring namespaces: the
<code>@namespace</code> rule</h2>
<p>The <code>@namespace</code> <a
href="http://www.w3.org/TR/CSS21/syndata.html#at-rules">at-rule</a>
declares a namespace prefix and associates it with a given namespace name
(a string). This namespace prefix can then be used in namespace-qualified
names such as the <a href="#css-qnames">CSS qualified names</a> defined
below.
<div class=example>
<pre>@namespace "http://www.w3.org/1999/xhtml";
<!-- -->@namespace svg "http://www.w3.org/2000/svg";</pre>
<p>The first rule declares a default namespace
<code>http://www.w3.org/1999/xhtml</code> to be applied to names that
have no explicit namespace component.
<p>The second rule declares a namespace prefix <code>svg</code> that is
used to apply the namespace <code>http://www.w3.org/2000/svg</code>
where the <code>svg</code> namespace prefix is used.
</div>
<p id=expanded-name-match>In CSS Namespaces, as in Namespaces in XML 1.0,
the prefix is merely a syntactic construct; it is the <em><dfn
id=expanded-name>expanded name</dfn></em> (the tuple of local name and
namespace name) that is significant. Thus the actual prefixes used in a
CSS style sheet, and whether they are defaulted or not, are independent
of the namespace prefixes used in the markup and whether these are
defaulted or not.
<div class=example>
<p>For example, given the following XML document:
<pre><!--
--><qml:elem xmlns:qml="http://example.com/q-markup"></qml:elem><!--
--></pre>
<p>and the following <code>@namespace</code> declarations at the
beginning of a CSS file:
<pre><!--
-->@namespace Q "http://example.com/q-markup";
<!---->@namespace lq "http://example.com/q-markup";<!--
--></pre>
<p>The selectors <code>Q|elem</code> and <code>lq|elem</code> in that CSS
file would both match the element <code><qml:elem></code>. (The
selector <code>qml|elem</code> would be invalid.)
</div>
<h3 id=syntax><span class=secno>3.1. </span>Syntax</h3>
<p>The syntax for the <code>@namespace</code> rule is as follows (using
the notation from the <a
href="http://www.w3.org/TR/CSS21/grammar.html">Grammar appendix of CSS
2.1</a> <a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>):
<pre><!--
-->namespace
<!-- --> : NAMESPACE_SYM S* [namespace_prefix S*]? [STRING|URI] S* ';' S*
<!-- --> ;
<!-- -->namespace_prefix
<!-- --> : IDENT
<!-- --> ;<!--
--></pre>
<p>with the new token:
<pre>@{N}{A}{M}{E}{S}{P}{A}{C}{E} {return NAMESPACE_SYM;}</pre>
<p>Any <code>@namespace</code> rules must follow all @charset and @import
rules and precede all other non-ignored at-rules and style rules in a
style sheet. For CSS syntax this adds <code>[ namespace [S|CDO|CDC]*
]*</code> immediately after <code>[ import [S|CDO|CDC]* ]*</code> in the
<code>stylesheet</code> grammar.
<p>A syntactically invalid <code>@namespace</code> rule (whether malformed
or misplaced) must be <a
href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>. A CSS
<a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">style
sheet</a> containing an invalid <code>@namespace</code> rule is not a <a
href="http://www.w3.org/TR/CSS21/conform.html#valid-style-sheet">valid
style sheet</a>.
<p>A URI string parsed from the <code>URI</code> syntax must be treated as
a literal string: as with the <code>STRING</code> syntax, no URI-specific
normalization is applied.
<p>All strings—including the empty string and strings representing
invalid URIs—are valid namespace names in <code>@namespace</code>
declarations.
<h3 id=scope><span class=secno>3.2. </span>Scope</h3>
<p>The namespace prefix is declared only within the style sheet in which
its <code>@namespace</code> rule appears. It is not declared in any style
sheets importing or imported by that style sheet, nor in any other style
sheets applying to the document.
<h3 id=prefixes><span class=secno>3.3. </span>Declaring Prefixes</h3>
<p>A <dfn id=namespace-prefix>namespace prefix</dfn>, once declared,
represents the namespace for which it was declared and can be used to
indicate the namespace of a namespace-qualified name. Namespace prefixes
are, <a href="http://www.w3.org/TR/CSS21/syndata.html#counter">like CSS
counter names</a>, case-sensitive.</p>
<!-- They do not, however, distinguish between equivalent
canonical Unicode representations. Essentially, an <code>@namespace</code>
declaration declares all prefixes that map to the same NFC representation as
the given prefix to the same namespace name. (See [[!UNICODE]] for the definition
of NFC normalization.) -->
<p>If in the namespace declaration the namespace prefix is omitted, then
the namespace so declared is the default namespace. The <dfn
id=default-namespace>default namespace</dfn> may apply to names that have
no explicit namespace prefix: modules that employ namespace prefixes must
define in which contexts the default namespace applies. For example,
following <a href="#XML-NAMES"
rel=biblioentry>[XML-NAMES]<!--{{!XML-NAMES}}--></a>, in Selectors <a
href="#SELECT" rel=biblioentry>[SELECT]<!--{{SELECT}}--></a> the default
namespace applies to type selectors—but it does not apply to attribute
selectors. There is no default value for the default namespace: modules
that assign unqualified names to the default namespace must define how
those unqualified names are to be interpreted when no default namespace
is declared.
<p class=note>Note that using default namespaces in conjunction with type
selectors can cause UAs that support default namespaces and UAs that
don't support default namespaces to interpret selectors differently.
<p>If a namespace prefix or default namespace is declared more than once
only the last declaration shall be used. Declaring a namespace prefix or
default namespace more than once is nonconforming.
</div>
<div>
<h2 id=css-qnames><span class=secno>4. </span>CSS Qualified Names</h2>
<p>A <dfn id=css-qualified-name>CSS qualified name</dfn> is a name
explicitly located within (associated with) a namespace. To form a
qualified name in CSS syntax, a namespace prefix that has been declared
within scope is prepended to a local name (such as an element or
attribute name), separated by a "vertical bar" (<code>|</code>, U+007C).
The prefix, representing the namespace for which it has been declared,
indicates the namespace of the local name. The prefix of a qualified name
may be omitted to indicate that the name belongs to no namespace, i.e.
that the namespace name part of the expanded name has no value. Some
contexts (as defined by the host language) may allow the use of an
asterisk (<code>*</code>, U+002A) as a wildcard prefix to indicate a name
in any namespace, including no namespace.
<div class=example>
<p>Given the namespace declarations:
<pre>@namespace toto "http://toto.example.org";
<!-- -->@namespace "http://example.com/foo";</pre>
<p>In a context where the default namespace applies
<dl>
<dt><code>toto|A</code>
<dd>represents the name <code>A</code> in the
<code>http://toto.example.org</code> namespace.
<dt><code>|B</code>
<dd>represents the name <code>B</code> that belongs to no namespace.
<dt><code>*|C</code>
<dd>represents the name <code>C</code> in any namespace, including no
namespace.
<dt><code>D</code>
<dd>represents the name <code>D</code> in the
<code>http://example.com/foo</code> namespace.
</dl>
</div>
<p>The syntax for the portion of a CSS qualified name before the local
name is given below, both for qualified names that allow wildcard
prefixes (<code>wqname</code>) and for qualified names that disallow
wildcard prefixes (<code>qname</code>). (The syntax uses notation from
the <a href="http://www.w3.org/TR/CSS21/grammar.html">Grammar appendix of
CSS 2.1</a>. <a href="#CSS21"
rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> Note this means that
comments, but not white space, are implicitly allowed between tokens.):
<pre><!--
-->qname_prefix
<!-- --> : namespace_prefix? '|'
<!-- --> ;
<!-- -->wqname_prefix
<!-- --> : [ namespace_prefix? | '*' ] '|'
<!-- --> ;
<!-- -->qname
<!-- --> : qname_prefix? ident
<!-- --> ;
<!-- -->wqname
<!-- --> : wqname_prefix? ident
<!-- --> ;<!--
--></pre>
<p>CSS qualified names can be used in (for example) selectors and property
values as described in other modules. Those modules must define handling
of namespace prefixes that have not been properly declared. Such handling
should treat undeclared namespace prefixes as a parsing error that will
cause the selector or declaration (etc.) to be considered invalid and, in
CSS, <a
href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
<div class=example>
<p>For example, the Selectors module <a href="#SELECT"
rel=biblioentry>[SELECT]<!--{{SELECT}}--></a> defines a type selector
with an undeclared namespace prefix to be an invalid selector, and CSS
<a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> requires
style rules with an invalid selector to be completely ignored.
</div>
</div>
<h2 class=no-num id=acknowledgments>Acknowledgments</h2>
<p>This draft borrows heavily from earlier drafts on CSS namespace support
by Chris Lilley and by Peter Linss and early (unpublished) drafts on CSS
and XML by Håkon Lie and Bert Bos, and XML Namespaces and CSS by Bert Bos
and Steven Pemberton. Many current and former members of the CSS Working
Group have contributed to this document. Discussions on www-style@w3.org
and in other places have also contributed ideas to this specification.
Special thanks goes to L. David Baron, Karl Dubost, Ian Hickson, Bjöern
Höhrmann, and Lachlan Hunt for their comments.
<h2 class=no-num id=references>References</h2>
<h3 class=no-num id=normative-references>Normative references</h3>
<!--begin-normative-->
<!-- Sorted by label -->
<dl class=bibliography>
<dd style="display: none"><!-- keeps the doc valid if the DL is empty -->
<!---->
<dt id=CSS21>[CSS21]
<dd>Bert Bos; et al. <a
href="http://www.w3.org/TR/2011/REC-CSS2-20110607"><cite>Cascading Style
Sheets Level 2 Revision 1 (CSS 2.1) Specification.</cite></a> 7 June
2011. W3C Recommendation. URL: <a
href="http://www.w3.org/TR/2011/REC-CSS2-20110607">http://www.w3.org/TR/2011/REC-CSS2-20110607</a>
</dd>
<!---->
<dt id=RFC2119>[RFC2119]
<dd>S. Bradner. <a href="http://www.ietf.org/rfc/rfc2119.txt"><cite>Key
words for use in RFCs to Indicate Requirement Levels.</cite></a> Internet
RFC 2119. URL: <a
href="http://www.ietf.org/rfc/rfc2119.txt">http://www.ietf.org/rfc/rfc2119.txt</a>
</dd>
<!---->
<dt id=XML-NAMES>[XML-NAMES]
<dd>Tim Bray; et al. <a
href="http://www.w3.org/TR/2009/REC-xml-names-20091208/"><cite>Namespaces
in XML 1.0 (Third Edition).</cite></a> 8 December 2009. W3C
Recommendation. URL: <a
href="http://www.w3.org/TR/2009/REC-xml-names-20091208/">http://www.w3.org/TR/2009/REC-xml-names-20091208/</a>
</dd>
<!---->
</dl>
<!--end-normative-->
<h3 class=no-num id=informative-references>Informative references</h3>
<!--begin-informative-->
<!-- Sorted by label -->
<dl class=bibliography>
<dd style="display: none"><!-- keeps the doc valid if the DL is empty -->
<!---->
<dt id=SELECT>[SELECT]
<dd>Tantek Çelik; et al. <a
href="http://www.w3.org/TR/2011/REC-css3-selectors-20110929/"><cite>Selectors
Level 3.</cite></a> 29 September 2011. W3C Recommendation. URL: <a
href="http://www.w3.org/TR/2011/REC-css3-selectors-20110929/">http://www.w3.org/TR/2011/REC-css3-selectors-20110929/</a>
</dd>
<!---->
</dl>
<!--end-informative-->
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