Think you're right about script 5. Similarly, script 6 is often used by save points to play the sound and the dialog about saving your game when you are stood inside the save point object. As far as I can remember, the difference between 5 and 6 is that 5 executes repeatedly, 6 only plays once (and won't execute again until you leave and re-enter the object, or line in this case).
Will have a further look, I'm just going to take a look at your questions.
[Edit]
Yes, one entity can define multiple LINEs and they will each exist & execute the relevant script, so there's no cancelling out of previous definitions. Only the PC activates the line (another entity crossing it won't activate it).
[Edit2]
Script 2: Activates once when a button is pressed.
Script 3: Activates once when you move into the object/line. When you stop, and then move again, the script activates (provided you're still in the object/line, of course).
Script 4: Not sure. Seems similar to 3
Script 5: Activates repeatedly whilst you are on the object/line.
Script 6: Activates once when you move into the object/line; will not reactivate until you leave and re-enter.
Script 7: Activates once only when you have left the object/line.
The remainder are not object/line-specific and won't be activated by any object movement. Of course any of these script numbers can be used for general-purpose scripts if it's not a visible entity.
[Edit3]
SLIDR is related to SOLID since it's the opcode before SOLID, and is used in conjunction with it in "condor1", a very simple field. It's used three times, once for each playable character that can be played during the game (Cloud, Tifa, Cid), along with the SOLID opcode in a separate script. Interestingly, it's SLIDR(0, 22) for Cloud and Cid (common after moving towards a ladder before LADER is called), and SLIDR(0,1E) for Tifa. It also comes after TALKR opcode. So I guess the question is, what is "R"
Here's the relevant script clips for some clarity. This is talking to the guy that wants help in Fort Condor, and having said yes, you'll help...
ojisan, Script 2:
WindowDialog(1,7) //“Really!? Then go on up and they'll fill you in on the details.â€
Request(cloud[3],5,REQ_SYNC) // See below
ObjectSolid(Off)
MovementSpeed(0,0,8)
ObjectMove(63,-45)
Request(cloud[4],5,REQ_SYNC) // See below
TLKON(1)
ObjectSolid(Off)
ObjectVisible(Off)
cloud, Script 3:
main:
ObjectSolid(Off)
return
cloud, Script 4:
main:
SLIDR(0,34) // 0x22
return
[Edit4]
Sorry for talking to myself.
I think it's Range - Talk Range, Solid Range. Still looking at it.