Optionaloccupiedcells to exclude - already taken by another feature, a monster, an item
Optionalterrainraw terrain kind ids eligible (indices into the Level's own kinds); omit for any kind
Optionalwithinrestrict the search to these cells (a room's interior, a hand-picked region); omit for the whole level
Filters over terrain and occupancy for a placement pool - the seam a dungeon's feature/content hooks use to ask "which cells could this go on" without
FeatureLayeror a game's own item/monster classes ever entering the picture. Every field is optional and narrows the pool further; omitting all of them is every cell on the level.