Everything in the room: 54 records of 32 bytes, all zero on the tape. The first six have fixed jobs -- the player's legs and body, two bolts he fires, two things fallen from the sky -- and the other 48 are the room's: the builder (BUILD_ROOM) fills them from the top down with scenery and objects, and QUEST_INTO_ROOM puts the quest things in the lowest free ones. The main loop (START) runs every record's update routine once a turn, in order, empty ones included.

A record: +0 the graphic, which also picks the update routine (UPDATES) and the sprite (GRAPHICS); 0 is an empty record, and 1 one that is emptied when it is next drawn. +1 to +3 U, V and Z. +4 and +5 the half-sizes in U and V, +6 the whole height from the base at +3. +7 the flags: bit 1 is set, among other uses, on the record being tested for overlaps (DO_ANY_OBJS_INTERSECT); bit 4 that it is to be drawn (LIST_DRAWN), bit 5 that it moved and its old picture must be wiped (RENDER_DYNAMIC_OBJECTS), bit 6 mirrored and bit 7 upside down (FIND_SPRITE); the rest are described with the routines that use them. +8 the room -- except for scenery, where it is the scenery entry's second byte: for a doorway the room it leads to, otherwise 0. +9 to +B the step in U, V and Z this turn. +C what it bumped into. +D bit 7: kills what it moves into; bit 5: kills what touches it; bit 6: killed. +E and +F an extra step in U and V, added into the next move and cleared (CALC_PLYR_DUV); a doorway uses it to steer the player to its middle (NUDGE_ALONG_V, NUDGE_ALONG_U).

+10 and +11: for a quest thing, the address of its quest record (QUEST_INTO_ROOM); other kinds keep their own counters there. +12 and +13 the drawing nudge, signed, added to the pixel x and y (CALC_PIXEL_XY); the update routines set it, through the short routines from DRAW_AT_L8 on. +14 to +17 are each kind's own; bit 7 of +17 is set on a record that meets the player's legs, or graphic 91, in Z -- one on top of the other (MARK_STOOD_ON) -- and LIFT, BOBBER and CRUMBLING_BLOCK read it. +18 and +19 the width in bytes and the height in rows of the sprite as last drawn, +1A and +1B its pixel x and y; +1C to +1F the same four from the turn before, copied there before each update (START) so the old picture can be wiped.