sub addInnerObj {
                my ($self, $index, @obj) = @_;

                #assert validity of objects pushed 
                #onto inner arrays-of-objects
                #my $constrAoAoObj = find_type_constraint('Obj');
                #for my $o (@obj) {                              
                        #$constrAoAoObj->assert_valid($o);       
                #}
                push @{ $self->arr2d->[$index] }, @obj;
        }