XML in a Nutshell, 3rd Edition

Binding Prefixes to URIs

Each prefix in a qualified name must be associated with a URI. For example, all XSLT elements are associated with the http://www.w3.org/1999/XSL/Transform URI. The customary prefix xsl is used in place of the longer URI http://www.w3.org/1999/XSL/Transform.

Tip

You can’t use the URI in the name directly. For one thing, the slashes in most URIs aren’t legal characters in XML names. However, it’s occasionally useful to refer to the full name without assuming a particular prefix. One convention used on many XML mailing lists and in XML documentation is to enclose the URI in curly braces and prefix it to the name. For example, the qualified name xsl:template might be written as the full name {http://www.w3.org/1999/XSL/Transform}template. Another convention is to append the local name to the namespace name after a sharp sign so that it becomes a URI fragment identifier. For example, http://www.w3.org/1999/XSL/Transform#template. However, both forms are only conveniences for communication among human beings when the URI is important but the prefix isn’t. Neither an XML parser nor an XSLT processor will accept or understand the long forms.

Prefixes are bound to namespace URIs by attaching an xmlns:prefix attribute to the prefixed element or one of its ancestors. (The prefix should be replaced by the actual prefix used.) For example, the xmlns:rdf attribute of this rdf:RDF element binds the prefix rdf to the namespace URI http://www.w3.org/TR/REC-rdf-syntax#: