[Zope-CMF] opaque items

[Miles]

Hi,

I'm looking at the callable opaque items and trying to understand when 
they might be used.  Apologies in advance for the vagueness of this 
question.

Has anyone got any ideas about what sort of situations it would be 
useful to use an ICallableOpaqueItem in - I'm having some trouble 
understanding what sort of general problem they solve / what the 
advantage is . . . and when you wouldn't use it!

Also, does anyone know of any examples of its use other than CMFUid and 
the CMF Discussion tool?  I think it might help if there was a bit more 
for me to look at . . .

Thanks for any opinions

Miles