Sighted events - Who does the seeing?

[Bob_The_Mighty]

Ive been toying with a stealth mod and I've been experimenting with ai behaviour, but there is one thing I cannot pin down. I can use sighted events or [filter_vision] to determine a unit that has been seen by the enemy, but I cannot determine which units are doing the seeing. In other words, I can store and manipulate the visible unit (Bob), but I can't find a reliable way to store and manipulate the unit/s that can see Bob.

Sighted events appear to have automatic variables ($x2,$y2), but the seeing unit may well not be in that hex when it completes its move. Besides, what happens if multiple units all see Bob at the same time? I've tried various combinations of unit and location filters, but none do the job. Can anyone suggest a solution or workaround?

A related issue concerns the player option to 'delay shroud updates'. The wiki says sighted events will be delayed for players until the option is turned off. I've tried to test that but it actually seems to work immediately, even when the option is turned on. Is the wiki out of date or did I misunderstand?

[vghetto]

Isn't second_unit always assigned even though $x2,$y2 are not?