Enemy-free area around staircases...

[Jarulf]

This does indeed happen.

It would seem reasonable, but as Mystery said, on dlvl 15 you get 4 big rooms, and one of the big rooms that has the stairway sometimes contains monsters. This usually happens when the stairs are very close to one corner of the room, IIRC, and the monsters would then be somewhere in the opposite corner or so. That made me think that there is a range check as well.

Strange that those special rooms mentioned in the first quote didn't get such a range check.

I don't think "room" always correspond well with visial "rooms" and walls. But I don't remember that much. The game uses a few different internal maps with various bits set for various things. One can relatively easy extract thm out at run time and have an external program plot them for show. Don't think I have any such program left though. In any case, the special rooms are if I recall correctly, the first ones placed (I would say stairs are first placed), then the type of the room is randomly chosen (I have mostly looked at church and cats here) and populated. Basically there is a sort of density value for each room type and the game simply crams in monsters and then eventual object (perhaps in other orther) into the room. I recall there being a bug even where the game (programmer) accessed the valeus incorrectly (there is different values for each difficulty as well) for one room type in the cats. Nothing major though. Caves are a bit special in that rooms can hev "walls" you can see and fire over/through. And it add some extra spice :)