Room Over Room
Room Over Room (ROR), also referred to as Sector Over Sector (SOS) and Floor Over Floor (FOF), is a technique in the BUILD Engine games used to simulate more realistic environments by displaying more than one sector over another in a vertical fashion to seamlessly create the appearance of a single area of higher complexity than is natively possible.
Examples of ROR applications are multi-level structures and things such as pools of liquids.
True Room Over Room is a feature new to EDuke32 that allows construction of multiple-level stacks directly on the side of the engine and map format. It is technologically distinct from the ROR used in Shadow Warrior, Blood, Redneck Rampage, the old cDuke port, and EDuke32's SE 40. Those implementations are "fake" because they are achieved using view portals and teleporters from the game code.