If the namespace attribute is present, then it also is interpreted as an attribute value template. The string that results
from instantiating the attribute value template should be a URI reference. It is not an error if the string is not a syntactically
legal URI reference. If the string is empty, then the expanded-name of the element has a null namespace URI. Otherwise, the
string is used as the namespace URI of the expanded-name of the element to be created.
Examples (xslt:xml): Overview 22:623:6