I'm (Bill Frantz) not sure I understand the problem. Perhaps a concrete example would help.
Let's see...
Suppose I wish to memory may an object, and I want a special keeper for it. For example, I'm doing networking coherency at the page level by juggling the page keys. Somebody hands me a segment key that they allege contains the pages for the object, and I wrap this segment with a red segment in order to place my keeper in control of it.
What happens if the segment I got handed implements its own internal
keeper logic isn't pretty. There is an ambiguity as to which keeper
(internal or mine) should be called. In some cases I may want both
the internal keeper and my own keeper called, and I might want them
called either top-down or bottom-up in the seg tree logic.
Jonathan