Each prefix is associated with a URI (technically a URI reference) called a namespace name.
For example, all elements in XSLT 1.0 style sheets are associated with the http://www.w3.org/1999/XSL/Transform URI.
The customary prefix xsl
is a shorthand for the longer URI
http://www.w3.org/1999/XSL/Transform.
You can't use the URI in the element name directly.
{http://www.w3.org/1999/XSL/Transform}template
http://www.w3.org/1999/XSL/Transform#template