BackPack
A list of Tile-stack objects currently being carried by the user. To show/hide backpack, press Ctrl+B. To cycle through contents of BackPack, press Tab/Shift+Tab. To use currently selected object in BackPack, press Enter (or click on it). To pick up a Tile-stack object and place it in BackPack, drag it to BackPack.
Room
A Room object is a rectangular region that can contain any or all of the aforementioned objects. Along any of its 4 walls it can contain 0 or more doors, which can be either open or closed.
Corridor
A Corridor object is a long, relatively narrow region with 2 walls on either side, and may have a wall at either end. It may contain doors/openings along any of its walls. The width of a Corridor object is generally a multiple of the default cell width (usually this multiple is 1 or 2). To travel down a Corridor, press an arrow key multiple times (or hold it down). To jump from one side of a vertically oriented Corridor to the other, press the Left/Right Arrow Key (or Up/Down if the orientation of the Corridor is horizontal).
Level
A Level object is a collection of Rooms, Corridors, and other objects. To display the entire Level at once, filling the screen, press Ctrl+Page Up. To return to a normal magnification level, press Ctrl+Page Down. There may be more than one level per game.