1. xmlns:a="" where namespace URI is null is not valid
2. xmlns:doc where xmlns is used as element prefix is not valid
3. xmlns:xmlns where xmlns is used as prefix is not valid
4. xmlns:xml="a" where xml is used as prefix but URI does not match the xml uri (http://www.w3.org/XML/1999/namespace) is not valid


git-svn-id: https://svn.apache.org/repos/asf/xerces/c/trunk@174407 13f79535-47bb-0310-9956-ffa450edef68