In release 1.0.1, setting these was silently ignored (which was itself technically a bug - see issue #46 for some background). In release 1.0.2 these cause an error because the default schema language is XSD.
Unfortunately its not possible at this time to apply a DTD to an arbitrary XML document as JAXP doesn't provide a means to do this. Research is been done on this as part of Java XML Validation Collection