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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>CSS Namespaces Module</title>
<link rel="stylesheet" type="text/css" href="../default.css">
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-ED">
</head>
<body>
<div class="head">
<!--logo-->
<h1>CSS Namespaces Module</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:</dt>
<!--
<dd><a href="[VERSION]">http://www.w3.org/TR/[YEAR]/PR-css3-namespace-[CDATE]/</a></dd>
-->
<dd><a href="http://dev.w3.org/csswg/css3-namespace/">http://dev.w3.org/csswg/css3-namespace/</a>
<dt>Latest version:</dt>
<dd><a href="http://www.w3.org/TR/css3-namespace/">http://www.w3.org/TR/css3-namespace/</a></dd>
<dt>Previous version:</dt>
<dd><a href="http://www.w3.org/TR/2008/CR-css3-namespace-20080523/">http://www.w3.org/TR/2008/CR-css3-namespace-20080523/</a></dd>
<dt>Feedback:</dt>
<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 rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/"
>archives</a>)
<dt>Editors:</dt>
<dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a></dd>
<dd><a href="http://annevankesteren.nl/about">Anne van Kesteren</a>, Opera Software ASA</dd>
<dt>Previous Editors:</dt>
<dd>Peter Linss, Netscape Communications</dd>
<dd>Chris Lilley, W3C</dd>
</dl>
<!--begin-copyright-->
<p>[Here will be included the file "../copyright.inc"]</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.</p>
<h2 class="no-num no-toc" id="status">Status of this document</h2>
<!--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>
<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>
<!--toc-->
<div>
<h2 id="intro">Introduction</h2>
<p><em>This section is non-normative.</em></p>
<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 ([[SELECT]]), 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.</p>
</div>
<div>
<h2 id="conformance">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>
<p>Conformance to CSS Namespaces is defined for two classes:
<dl>
<dt><dfn>style sheet</dfn></dt>
<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>interpreter</dfn></dt>
<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.)</dd>
</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. [[!RFC2119]]</p>
<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.</p>
</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.</p>
<h3 id="terminology">Terminology</h3>
<p>Besides terms introduced by this specification, CSS Namespaces uses the
terminology defined in Namespaces in XML 1.0. [[!XML-NAMES]] 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>
<p>In CSS Namespaces a namespace name consisting of the empty string is
taken to represent the null namespace or lack of a namespace.</p>
<div class="example">
<p>For example, given the namespace declarations:</p>
<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.</p>
</div>
</div>
<div>
<h2 id="declaration">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.</p>
<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>
<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.</p>
</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.</p>
<div class="example">
<p>For example, given the following XML document:</p>
<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:</p>
<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.)</p>
</div>
<h3 id="syntax">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> [[!CSS21]]):</p>
<pre><!--
-->namespace
<!-- --> : NAMESPACE_SYM S* [namespace_prefix S*]? [STRING|URI] S* ';' S*
<!-- --> ;
<!-- -->namespace_prefix
<!-- --> : IDENT
<!-- --> ;<!--
--></pre>
<p>with the new token:</p>
<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>
<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>
<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>
<p>All strings—including the empty string and strings representing
invalid URIs—are valid namespace names in <code>@namespace</code>
declarations.</p>
<h3 id="scope">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.</p>
<h3 id="prefixes">Declaring Prefixes</h3>
<p>A <dfn>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>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 [[!XML-NAMES]], in
Selectors [[SELECT]] 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>
<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>
<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.</p>
</div>
<div>
<h2 id="css-qnames">CSS Qualified Names</h2>
<p>A <dfn>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.</p>
<div class="example">
<p>Given the namespace declarations:</p>
<pre>@namespace toto "http://toto.example.org";
<!-- -->@namespace "http://example.com/foo";</pre>
<p>In a context where the default namespace applies</p>
<dl>
<dt><code>toto|A</code></dt>
<dd>represents the name <code>A</code> in the <code>http://toto.example.org</code>
namespace.</dd>
<dt><code>|B</code></dt>
<dd>represents the name <code>B</code> that belongs to no namespace.</dd>
<dt><code>*|C</code></dt>
<dd>represents the name <code>C</code> in any namespace, including no
namespace.</dd>
<dt><code>D</code></dt>
<dd>represents the name <code>D</code> in the <code>http://example.com/foo</code>
namespace.</dd>
</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>. [[!CSS21]] Note this means that comments, but not white space,
are implicitly allowed between tokens.):</p>
<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>.</p>
<div class="example">
<p>For example, the Selectors module [[SELECT]] defines a type selector with
an undeclared namespace prefix to be an invalid selector, and CSS
[[!CSS21]] requires style rules with an invalid selector to be completely
ignored.</p>
</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.</p>
<h2 class="no-num" id="references">References</h2>
<h3 class="no-num" id="normative-references">Normative references</h3>
<!--begin-normative-->
<p>[Here will be inserted the file "normative.inc"]</p>
<!--end-normative-->
<h3 class="no-num" id="informative-references">Informative references</h3>
<!--begin-informative-->
<p>[Here will be inserted the file "informative.inc"]</p>
<!--end-informative-->
</body>
</html>
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