Dispatches allocations (and deallocations) between two allocators (SmallAllocator and LargeAllocator) depending on the size allocated, as follows. All allocations smaller than or equal to threshold will be dispatched to SmallAllocator. The others will go to LargeAllocator.
A Segregator with more than three arguments expands to a composition of elemental Segregators, as illustrated by the following example: