No, that's fine, Lars, I forgot that rel_segs show up in that denormalized table. Had to so existing code would work.
Peter - checking for membership_rel (rather than group_id = container_id) is the conceptually correct thing to do, because the "registered users" view is meant to be "all members of the registered users group" which is defined as those with membership_rel.
The other works but is more obscure IMO.