SWAP WORLD "file"
Swap world is a MegaZeux command that swaps the current MZX world with the one stated. Its syntax is SWAP WORLD "filename".
In the earlier days of MegaZeux, having large MZX worlds could cause instability, so it was often necessary to partition large games into several worlds even before hitting MZX's board limit. Upon swapping worlds, all "state" information in the current world will be thrown out, essentially resetting that world to its original state. However, all of the values for global counters are retained. This is often exploited to quickly and easily "reset" levels, as swapping a world to itself is valid. (The best-known example of this is MZX Combat Trainer.)
The existence of this command is why no load_world function counter exists.