Describing Processing

Moving Power from the Programmers... without ticking them off

Control over Components XPDL allows class designers to specify constraints, attributes, entities, and notations processing separately. (There is a convenient 'all' as well.) Each may be required or not required.
Breaking Down Monoliths While attribute defaults are still locked into schemas, there is no good reason for entity declarations to be mixed with structural info. This makes it easy to reference entities (and notations) separately.
Flexibility Want your attribute values but aren't worried about validation? Finally, a solution that's reliable! (Plus, you can mix and match schemas and DTDs.)