The scripting command SetChar has the opcode (0x0F).
- Byte - Selected character
This opcode sets an internal "current character" flag used by several other operations.
If the argument is 0, the selected character is effectively "all". If the selected character is 7, then a random character is chosen. If greater than 7, then it asks in the exact same way as it would for WhoWill.
It seems that when a number n is set, the n first characters are concerned. See the holes in Yak Temple (X=5 Y=12 for example) when no levitate. The command is "SetChar 2" and the 2 first characters receive damages.
This does not, in fact, set the selected character. If the argument is 1-6, it reads the byte, but then does nothing. This may actually have been a bug, but since this command is only ever used to force events back to "select all" states (with an argument of 0) in the Xeen games, it probably went unnoticed.