Behaviour of AAs after initialization

[via Digitalmars-d]

AAs are (like regular dynamic arrays) initialized to `null`. On 
first modification (i.e. assignment of an element), memory is 
allocated and the AA variable updated to point at it.

However, is there a guarantee that AAs are never reallocated once 
they are initialized, i.e. is it then safe to assume that changes 
made through a copy of an AA variable (e.g. pass by value) are 
visible through the original variable?

The current implementation behaves like this, but the language 
reference does not mention it, AFAICS. I'd like to amend the 
documentation if this behaviour is reliable.

This is the thread where the question came up:
http://forum.dlang.org/post/qnllglkrrgfdpwbmvwsp@forum.dlang.org
http://forum.dlang.org/post/tguaxwqijnkqszghauia@forum.dlang.org