[relax-ng] Green to Blue?

Some thougths on questions from potential users about 
validating with both RELAX and DTD.

In the business world - we'd like to decouple the validation of the
physical XML instance from the validation engine.

I.e. I build a piece of XML using my RELAX tools and send it to 
someone - who only has a DTD valdiator and therefore just 
applies that validation.

This all comes back to the PI header in the XML just containing
a neutral reference - and the people can resolve that then
to either a RNG schema or a DTD or whatever - depending on
their own local validator.

Its an abstraction of the validation structure that is resolved by
the user.  Is this even something we want to encourage?

Thoughts?

Thanks, DW.