27 addresses, indexed by the Z code (0 the candidate above, 1 overlapping, 2 IY above) + the V code (0 the candidate further back, 3 overlapping, 6 IY further back) + the U code (0 IY further back, 9 overlapping, 18 the candidate further back), as SORT_AND_DRAW works them out. "Further back" is smaller U, larger V, lower Z. The table is Knight Lore's, entry for entry.

Four outcomes. IY_GOES_FIRST when IY is behind or level with the candidate on all three axes and strictly behind on at least one: IY must be drawn first. CANDIDATE_ALREADY_FIRST for the mirror image, where the candidate is behind IY and is being drawn first anyway. ORDER_UNCONSTRAINED where each is in front of the other on some axis, which says nothing about their order. BOXES_INTERSECT, index 13, for boxes that overlap on every axis. The last three do the same thing.