This function is not called in assignments by reference and otherwise
indirect changes to array dimensions overloaded with
ArrayAccess (indirect in the sense they are
made not by changing the dimension directly, but by changing a
sub-dimension or sub-property or assigning the array dimension by
reference to another variable).
Instead, ArrayAccess::offsetGet() is called. The
operation will only be successful if that method returns by reference,
which is only possible since PHP 5.3.4.