Usage:
A prefixed namespace is considered to apply to the current and all child elements and attributes that have been declared specifying the same prefix.
Notation:
<pre:name xmlns:pre="http://www.test.com/" pre:attname="whatever">
Prefixed namespace values can be redeclared.
pre:name - is called a QName.
Only since XML 1.1 is it allowed to undeclare prefixed namespaces using 'xmlns:pre=""'.
The prefix functions only as a placeholder for a namespace uri.
The prefix is not significant, although it is not recommended different prefixes can be defined in the same document mapping to the same namespace uri.
Constraints:
“Prefixes beginning with the three-letter sequence x, m, l, in any case combination, are reserved for use by XML and XML-related specifications.”