The 500 hats of the standard allocator

The standard allocator model must have seemed amazing in 2011. We're about to see how, with just one C++ type, we can accomplish all of the following feats:

• Specify a memory resource to be used for allocating memory.
• Annotate each allocated pointer with some metadata that will be carried along
  for its whole lifetime, all the way to deallocation time.
• Associate a container object with a particular memory resource, and make sure
  that association is "sticky"--this container object will always use the given
  heap for its allocations.
• Associate a container value with a particular memory resource, meaning
  that the container can be efficiently moved around using value semantics without
  forgetting how to deallocate its contents.
• Choose between the two mutually exclusive behaviors above.
• Specify a strategy for allocating memory at all...