Yes, you are right of course. I initially was mixed up over whether this was a replacement for just the schema definition or for XML itself too. I also thought YAML would be the choice then but RELAX seems to borrow from regular expressions which is nice, and I don't quite see how to link various YAML documents in a YAML stream to a RELAX definition.
Actually I was most impressed that there are java tools that will generate classes based on RELAX NG definitions. Which made me think RELAX-like language might be very nice as a way to quickly define lots of things, like classes, db schemas, business logic, etc. I have to study it more to really understand how far it goes though. There are so many meta description languages out now for small domains so I had a hope. Not too long ago I was looking at some of the modules that help you design classes quickly in Perl but every module has its pros and cons of course. Thank you and all other posters.