namespace-uri-for-prefix($prefix as xs:string?, $element as element()) xs:anyURI?
Returns the namespace URI of one of the in-scope namespaces for $element, identified by its namespace prefix.
If $element has an in-scope namespace whose namespace prefix is equal to $prefix, it returns the namespace URI of that namespace. If $prefix is the zero-length string or the empty sequence, it returns the namespace URI of the default (unnamed) namespace. Otherwise, it returns the empty sequence.
Prefixes are equal only if their Unicode code points match exactly.
