With this function you can check and see whether the room you specify exists or not. This function takes the room index (a real number) and not the room name (a string). This function is most useful when you are creating rooms dynamically using the function room_add, but you can also use the read only variables room_first and room_last or the functions room_next and room_previous to get a specific room index, or provide a variable that has stored the index of any other room in your game.
Argument Description index The index of the room to check.
The above code checks to see if the room indexed in the array "global.rm" exists and if it does it then goes to that room.