In the editor, when you give an Object an effect it can can be triggered to carry out, you often choose both an Action (for example Take All These from Area, Let Player Shoot Weapon, Change Player Intelligence, etc.) and a specific setting for that Action (for the examples above, they could be: Dogs, Ship’s Cannon, and +15, respectively). But you don’t have to be this precise with every object you create in the editor before actually building your rooms and regions.
With Custom Spaces and Custom Obstacles (their categories appear with a * after them when you’re scrolling through Object categories), you still specify an Action for the object, but the specific part is left as “(SET LATER)” by default. “SET LATER” means when you place one of the Custom Objects or Obstacles in a room, THEN you set the specific effect for that object. Each time you place a new copy of a Custom Space/Obstacle in a room, you can specify a different specific effect for that copy.
For instance, you could make a “Library Shelf” Custom Space that has passibilty set to NOTHING (the player can never move through it) and that’s triggered by bumping into it and has “Play Long Message” as its Action. Then, each time you place another Library Shelf in a room, you can choose a different long message that particular Library Shelf will display when the player bumps into it.
ACK comes with some pre-made Custom Spaces such a “Give Item” Custom Space, “Take Item” Custom Space, “Rid Room of…” Custom Space, etc. that you’re sure to get lots of milage from.