THE XML REVOLUTION - TECHNOLOGIES FOR THE FUTURE WEB

Namespace declarations

Namespaces are declared by special attributes and associated prefixes:

<... xmlns:foo="http://www.w3.org/TR/xhtml1"> ... <foo:head>...</foo:head> ... </...>

`<... xmlns:foo="http://www.w3.org/TR/xhtml1"> ... <foo:head>...</foo:head> ... </...>`

xmlns:prefix="URI" declares a namespace with a prefix and a URI:

the scope of declaration is lexical, the element containing the declaration and all descendants can be overridden by nested declaration
both element and attribute names can be qualified with namespaces
the name of the prefix is irrelevant - applications should use only the URI

For backward compatibility and simplicity, unprefixed element names are assigned a default namespace:

declaration: xmlns="URI"
default value: "" (means: treat as unqualified name)
does not affect unprefixed attribute names (they belong to the containing elements)

WidgetML with namespaces:

<widget xmlns="http://www.widget.org" xmlns:xhtml="http://www.w3.org/TR/xhtml1" type="gadget"> <head size="medium"/> <big><subwidget ref="gizmo"/></big> <info> <xhtml:head> <xhtml:title>Description of gadget</xhtml:title> </xhtml:head> <xhtml:body> <xhtml:h1>Gadget</xhtml:h1> A gadget contains a big gizmo </xhtml:body> </info> </widget>