Custom complex type libraries

RELAX NG allows one write custom type libraries for simple data types 
(i.e. PCDATA) in a variety of programming languages. Does this also 
extend to complex types, or is there any equivalent? For instance, could 
I write Java code to verify that the name of every child element was the 
name of a field in a particular table? (I don't really need to do that. 
It's just one example of something you can't do in pure RELAX NG that 
you could do in Java. There are many other possibilities.)

-- 
Elliotte Rusty Harold  [email protected]
XML in a Nutshell 3rd Edition Just Published!
http://www.cafeconleche.org/books/xian3/
http://www.amazon.com/exec/obidos/ISBN=0596007647/cafeaulaitA/ref=nosim