Allow themed rooms to be specified as joined to the rest of the level, but only at preexisting doors on the edge of the room, and the level generator should not create new doors to connect it to the rest of the level. Internally, this means expanding a room’s ‘joined’ variable from a boolean to a larger type that can hold a third value. This would be useful for making themed rooms where it’s desirable to connect them to the map only at specific points.