A prefixed namespace is considered to apply to the current and all child elements and attributes that have been declared specifying the same prefix.
<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.
“Prefixes beginning with the three-letter sequence x, m, l, in any case combination, are reserved for use by XML and XML-related specifications.”