Returns the prefixes of the in-scope namespaces for an element node.
fn:in-scope-prefixes( $element as element()xs:string*The function returns a sequence of strings representing the prefixes of the in-scope
namespaces for $element.
For namespace bindings that have a prefix, the function returns the prefix as an
xs:NCName. For the default namespace, which has no prefix, it returns
the zero-length string.
The result sequence contains no duplicates.
The ordering of the result sequence is implementation-dependent.
The XML namespace is in scope for every element, so the result will always include the string "xml".