[XML-SIG] XML Schema validator?

[Michael McLay]

I'm looking for a validator for XML Schema instance files.  
The XML Schema validator at http://www.ltg.ed.ac.uk/~ht/xsv-status.html 
is close to what I need, but it has a GPLed copyright on the validator
and a non-commercial restriction on the PyXML module that it is
dependant on.  The ideal mechanism for checking XML files against an
XML Schema would be built on top of the standard Python 1.6 XML
package and it would have a Python-like copyright.