Work Units clarification question

In the defn of a Work-Unit in CDL (latest draft) it says (on page 29 of 
the pdf):

"A Work Unit completes successfully when all its enclosed actions 
complete successfully."

Moving forward a little to consider multiple concurrent participants in 
a work unit that might have this new "concurrent" attribute (and 
possibly other things) what does "complete successfully" mean with 
respect to the concurrent activities.

For example if within such a work-unit 5 sub choreographies are now 
activated when does the parent "complete"?
Is it immediately the final sub-choreo starts or is it when the final 
sub-choreo also completes?
How does the termination status of a sub-choreo, in this scenario, 
affect the parent (i.e. a sub-choreo goes into an exception block)?

Cheers

Steve T