For an allocator A<T> which defines A<T>::pointer to a class type, i.e. not T*, I see no requirement that A<T>::pointer is convertible to A<U>::pointer, even if T* is convertible to U*. Such conversions are needed in containers to convert from e.g. ListNodeBase* to ListNode<T>*.

The obvious way to do such conversions appears to be pointer_traits::pointer_to(), but that's ill-formed if the static member function A<T>::pointer::pointer_to() doesn't exist and the allocator requirements don't mention that function, so you need to cast A<T>::pointer to A<T>::void_pointer then cast that to A<U>::pointer.

Is converting via void_pointer really intended, or are we missing a requirement that pointer_traits<A<T>::pointer>::pointer_to() be well-formed?

Proposed resolution:

Add to the Allocator requirements table the following requirement:

The expression pointer_traits<XX::pointer>::pointer_to(r) is well-defined.