[Boost-users] How are template arguments to rbtree_best_fit resolved

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 declaring 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?