[ubl-cmsc] ebXML as basis for UBL context work?

Okay, we're ready to move forward on discussing rhe individual issues!
Here's the first one. I'll send off the others in separate threads so that
the discussion stays structured.

1) Do we consider the "Document Assembly and Context Rules" document from
Vienna (v1.04) to be the starting point for our work, which we will be
refining? Or so we want to start from a clean slate and pull in input from
the document as needed? The question here is whether people consider the
Vienna work to be deeply broken in some way or whether it simply needs to be
finalized.