legitimate use of STL allocators: Scott Meyers

Question

I am reading effective STL by Scott Meyers and Item 11 has below text regarding allocators.

utility of allocators, suppose you have two heaps, identified by the classes Heap1 and Heap2. Each heap class has static member functions for performing allocation and deallocation:

class Heap1 {
public:
…
static void* alloc(size_t numBytes, const void *memoryBlockToBeNear); static void dealloc(void *ptr);
…
};
class Heap2 { ... }; // has the same alloc/dealloc interface

Further suppose you'd like to co-locate the contents of some STL containers in different heaps. Again, no problem. First you write an allocator designed to use classes like Heap1 and Heap2 for the actual memory management

template<typenameT, typename Heap>
SpecificHeapAllocator {
public:
pointer allocate(size_type numObjects, const void *localityHint = 0)
{
return static_cast<pointer> (Heap::alloc(numObjects * sizeof(T),
localityHint));
}
void deallocate(pointer ptrToMemory, size_type numObjects)
{
Heap::dealloc(ptrToMemory);
}
…
};

Then you use SpecialHeapAllocator to cluster containers' elements together:

vector<int, SpecificHeapAIlocator<int, Heap1 > > v; // put both v's and set<int, SpecificHeapAllocator<int Heap1 > > s; //s's elements in
//Heap1
list< Widget,
SpecificHeapAllocator<Widget, Heap2> > L; // put both L's and
map< int, string, less<int>, // m's elements in
SpecificHeapAllocator<pair<const int, string>, // Heap2
                                       Heap2> > m;

In this example, it's quite important that Heap1 and Heap2 be types and not objects. The STL offers a syntax for initializing different STL containers with different allocator objects of the same type, but I'm not going to show you what it is. That's because if Heap1 and Heap2 were objects instead of types, they'd be inequivalent allocators, and that would violate the equivalence constraint on allocators.

My questions on above is

1. What is STL syntax for "initializing different STL containers with different allocator objects of the same type"?

2. Why if Heap1 and Heap2 are objects they are inequivalent allocators?