A function included in the GECK version 184.108.40.206.
This is one of 4 functions which can be used to increase the game's performance in situations where many actors are in combat or otherwise doing complex pathing. Note that the flag is cleared every frame, so this function needs to be called in a script running on a reference in the loaded area.
When the SetAllVisible flag is set, actors do not perform LineOfSight checks. When actors check to see if they can see something, they assume they can see its head.