Try xsltproc (part of libxslt distro) and see what it does. If it works and ns_xml doesn't then my code could use improvement in which case send me example files and I'll try to dig in.
If it doesn't then it means that it hasn't been implemented in libxslt itself (which is still in heavy developement stage). For info on libxslt you should go to http://xmlsoft.org/XSLT/. If you have questions about how it works your best bet is to ask on their mailing list. ns_xml is just a wrapper.
