CSS Namespaces Module Level 3

• 1 Introduction
• 2Conformance
  • 2.1 Terminology
• 3Declaring namespaces: the @namespace rule
  • 3.1 Syntax
  • 3.2 Scope
  • 3.3 Declaring Prefixes
• 4 CSS Qualified Names
• Changes
• Acknowledgments
• References
  • Normative References
  • Informative References
• Index
• Property index

3 Declaring namespaces: the @namespace rule

The @namespace at-rule 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 CSS qualified names defined below.

  @namespace "http://www.w3.org/1999/xhtml";
  @namespace svg "http://www.w3.org/2000/svg";

In CSS Namespaces, as in Namespaces in XML 1.0, the prefix is merely a syntactic construct; it is the expanded name (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.

  <qml:elem xmlns:qml="http://example.com/q-markup"></qml:elem>

  @namespace Q "http://example.com/q-markup";
  @namespace lq "http://example.com/q-markup";

3.1 Syntax

The syntax for the @namespace rule is as follows (using the notation from the Grammar appendix of CSS 2.1 [CSS21]):

  namespace
    : NAMESPACE_SYM S* [namespace_prefix S*]? [STRING|URI] S* ';' S*
    ;
  namespace_prefix
    : IDENT
    ;

with the new token:

@{N}{A}{M}{E}{S}{P}{A}{C}{E} {return NAMESPACE_SYM;}

Any @namespace 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 [ namespace [S|CDO|CDC]* ]* immediately after [ import [S|CDO|CDC]* ]* in the stylesheet grammar.

A syntactically invalid @namespace rule (whether malformed or misplaced) must be ignored. A CSS style sheet containing an invalid @namespace rule is not a valid style sheet.

A URI string parsed from the URI syntax must be treated as a literal string: as with the STRING syntax, no URI-specific normalization is applied.

All strings—including the empty string and strings representing invalid URIs—are valid namespace names in @namespace declarations.

3.2 Scope

The namespace prefix is declared only within the style sheet in which its @namespace 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.

3.3 Declaring Prefixes

A namespace prefix, 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, like CSS counter names, case-sensitive.

If in the namespace declaration the namespace prefix is omitted, then the namespace so declared is the default namespace. The default namespace 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.

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.

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.

4 CSS Qualified Names

A CSS qualified name 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"(|, 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 (*, U+002A) as a wildcard prefix to indicate a name in any namespace, including no namespace.

  @namespace toto "http://toto.example.org";
  @namespace "http://example.com/foo";

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 (wqname) and for qualified names that disallow wildcard prefixes (qname). (The syntax uses notation from the Grammar appendix of CSS 2.1. [CSS21] Note this means that comments, but not white space, are implicitly allowed between tokens.):

  qname_prefix
    : namespace_prefix? '|'
    ;
  wqname_prefix
    : [ namespace_prefix? | '*' ] '|'
    ;
  qname
    : qname_prefix? ident
    ;
  wqname
    : wqname_prefix? ident
    ;
  wqwname
    : wqname_prefix? [ ident | '*' ]
    ;

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, ignored.

Changes

Changes made since the 29 September 2011 Recommendation:

• Added predefined qname, wqname, and wqwname productions, to make those constructs easier for other specs to use.

Acknowledgments

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, Björn Höhrmann, and Lachlan Hunt for their comments.

References

Normative References

Informative References

Index

Property index