I have been doing some research on AI Scripts in the HPS games for a future addition to the ACWCO Engineering pages. Don't know much about the BG system but here are some things I learned about them in the HPS games.
From the Editor Help file notes
"If an A/I Value different from 2 is defined for one or both sides, then the Flags value will be important. A value of 1 indicates that the A/I should not commit the entire side to the Attack or Defense, but should only commit forces based on opportunities. A value of 0 will cause the A/I to commit the entire side to the Attack or Defense."
I have not finished my testing on this but I can tell you for sure that if the AI value is set to 4 and the flag is set to 0 the AI will completely ignore any defensive scripts. I wrote a script calling for one dug in group to defend one flank while the remainder of the army attacked the other flank. When I attempted to test this one I was surprised to see the AI moving units from their breastworks and trying to cross a river to attack. When I looked at the Header Dialog I discovered the AI Value was 4 and the Flag 0, apparently I had forgotten to set them when setting up the scenario. So if you're going to use a 3-4 AI setting I suggest you set the flag to 1.
I also have not yet tested to determine if the AI will follow scripts at all if the value is set to anything other than 2 and the Help files are not completely clear on this matter.
Regarding scripts however the Help file does state that
"An A/I value of 2 indicates that the side should not initiate any A/I orders on its own. This value is best used when A/I Scripts are going to be defined for the scenario."
I have found this to be true. If units without scripts are attacked the AI will move them but if they are left alone they will sit in place and do nothing other than fire at opportunity targets. According to the Help files there is a way around this, the No Order script order.
"No Order - this Order should always have the objective (-1, -1). This Order indicates that the organization should not move or fire except as a response to an attack on itself. However, if a Brigade has this Order and its leader is currently mounted, then the A/I considers that Brigade to be "in reserve" and may automatically order it to defend a threatened Objective."
Once again I have not tested this one yet.
Gen. Ken Miller
AoP
