5. Specifying namespaces

5. Specifying namespaces
	Chapter 4. Other extensions

Namespace support in CSS3 style sheets is outlined in Selectors. In summary:

@namespace rule declares a namespace prefix and associates it to the namespace URI. Examples:
```
@namespace url(http://www.xmlmind.com/xmleditor/schema/configuration);

@namespace html url(http://www.w3.org/1999/xhtml);
```
Rule #1 specifies that element names (in selectors) without an explicit namespace component belong to the "http://www.xmlmind.com/xmleditor/schema/configuration" namespace.
Rule #2 specifies that element or attribute names with a "html" prefix belong to the "http://www.w3.org/1999/xhtml" namespace.
Notation for qualified names is prefix|local_name, where character '|' is used to separate the two parts of the qualified name.
Example of element names:
```
@namespace ns url(http://www.ns.com);

ns|para { font-size: 8pt;  }
ns|*    { font-size: 9pt;  }
|para   { font-size: 10pt; }
*|para  { font-size: 11pt; }
para    { font-size: 11pt; }
```
Rule #1
will match only para elements in the "http://www.ns.com" namespace.
Rule #2
will match all elements in the "http://www.ns.com" namespace.
Rule #3
will match only para elements without any declared namespace.
Rule #4
will match para elements in any namespace (including those without any declared namespace).
Rule #5
is equivalent to the rule #4 because no default namespace has been defined.
Examples of attribute names:
```
@namespace ns "http://www.ns.com";

[ns|role=minor] { font-size: 8pt; }
[*|role]        { font-size: 9pt; }
[|role]         { font-size: 10pt; }
[role]          { font-size: 10pt; }
```
Rule #1
will match only elements with the attribute role in the "http://www.ns.com" namespace with the value "minor".
Rule #2
will match only elements with the attribute role regardless of the namespace of the attribute (including no declared namespace).
Rule #3 and #4
will match only elements with the attribute role where the attribute is not declared to be in a namespace.
Note that default namespaces do not apply to attributes.
The attr() pseudo-function also supports namespaces.
```
@namespace ns "http://www.ns.com";

para:before { content: attr(ns|role); }
```
The generated content inserted before "para" elements is the content of attribute role declared in the "http://www.ns.com" namespace.


4. Styling an element which contains a specific child element		6. Inserting in generated content the name of the element which is the target of the CSS rule