Hi Theo:

have you already thought about the design of an extension feature for DIs?

See: http://sourceforge.net/tracker/?atid=503809&group_id=63395&func=browse

When we extend the concrete cd with a new feature, we may want to extend
the current DI with the essence of the new feature and then map the extended DI to the 
new concrete cd.

-- Karl

See also:
/proj/adaptive/www/design-decisions/plug-and-play/interface-classgraphs
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Difference between Curtis Clifton's approach
(see his PhD thesis) and Demeter interfaces:

we would have to specify for each traversal which visitors it wants to accept.
Or are those visitors only spectators? They may update the object being traversed
so they are more than spectators, they are assistants.

But many visitors can be made assistants by introducing stack structures 
to the visitor: see the capacity constraint checker for nested
containers.