Providing Extensibility

We don't know everything...

Leaving Room for the Future While I've tried hard to figure out what information belongs in a document class description, there's probably more out there.
Extensibility as Architectural Component By leaving the door open here - and by not requiring XPDL processors to understand any of the contents in this area - it remains possible for developers to add their own information to XPDs. By building this in at the beginning, rather than waiting for problems, we can learn from application developers what belongs in these documents.