Custom Edition maps are loaded from the custom_maps folder, as level
custom_maps\<name>, apart from the game's own maps of the same name. The
map lists get CUSTOM SINGLEPLAYER and CUSTOM MULTIPLAYER, by the scenario
type in the map: a custom singleplayer map plays as a campaign level, or
as network co-op from the Map screen; a custom multiplayer map plays as a
multiplayer map. A map with an OpenSauce header that asks for nothing of
OpenSauce's runs as stock Custom Edition runs it.