[Boost-users] Possibly too newbie a question?

I haven't received any response to my question. If this is is not the appropriate forum I would appreciate some suggestions as to where to ask the question. I have gone over the mailing list groups page and this seems to be the place to ask it but I could be wrong. I am stepping through interprocess shared memory code and I was a little confused by the offset_ptr code that I was hitting*. I cannot figure out how that is specified to the template of rbtree_best_fit. I see in boost/interprocess/interprocess_fwd.hpp the declaration of managed_shared_memory by typedef'ing basic_managed_shared_memory with rbtree_best_fit as the AllocationAlgorithm argument but I can't figure out how offset_ptr is is supplied as the VoidPointer argument to the rbtree_best_fit template. That template has 3 arguments but the forward declaration only provides one. Are the other two somehow inferred? If so, how? * I have looked at the documentation for interprocess - including the explanation of offset_ptr. I understand the need for it. I just don't see how it is incorporated into the rbtree_best_fit template.