[xliff] Schema validation

Hi all,

Does anyone know of a reliable XML schema validator that can *really*
validate a document that uses different namespaces?

- XMLSpy 4.4 is giving me "valid" results for documents that have test cases
of invalid non-XLIFF content.
- MSXML gives me various strange errors on valid documents.

We can make examples, but if we can't valid them they're not going to be
very helpful.
Any pointer would be welcome.

Thanks
-yves