as requires a
class or (COM) interface as the first argument and a class or interface reference as the second.
child as super is equivalent to the expression and statement:
super(child) if not assigned(child) and_then not child is super then begin raise exception.create(sErrInvalidTypecast); end;
However, trying to de-reference
nil by attempting to access an attribute or method will cause a RTE.
as ensures a typecast is legit.
as is one of the operators that can not be overloaded.