.spl files extended headers "location" table.

[Jarno Mikkola]

As you can see, the bit 0x0002 is called "Location" in IESDP, but there's nothing that says what that actually means, the Near Infinity has this data:

Where the 2 is the spellbook tab(F7), and the 4 is the Special Ability(F12) location. I honestly can't say what the others are for sure, but the item (3) should be obvious(F9-F11) as well as weapon (1) should be too(F2 - F6, depending on how many primary weapons the char has according to it's class). I would also assume the reserved (5) is for Bard songs, clerics turn undead and shamans dance... but who knows.

[Bubb]

1) Weapon abilities, (right-click quick weapon in inventory -> Abilities), or right-click weapon in actionbar, (F2-F5 depending on class). Only functions in a weapon's item ability header.

2) Spell, (F7 in actionbar). Only functions in a spell's ability header.

3) Item, (F8 in actionbar). Only functions in an item's ability header.

4) Ability, (F12 in actionbar). Only functions in a spell's ability header.

Other values do not function, and the associated ability will not appear anywhere. The only flexibility of this field is being able to change where spells appear, (Spell vs Ability) — and, on weapons, differentiating between weapon abilities and item abilities. Otherwise, you are locked to the relevant type.

So, pretty straightforward.

[kjeron]

A weapons first ability header is always treated as a weapon ability, regardless of it's ability location. It still affects it's presence on the action bar, and whether it can be activated as an item.  A weapons additional abilities are locked into their location function.

A spells ability location is not considered when selecting spells through op214(select spell) or op234/257 (contingency/sequencer creation), allowing spells that can be known/memorized but not cast unless through one of those opcodes.  Also useful if you're creating a custom identify spell that can only be accessed through the inventory UI - more or less how the vanilla identify spell functions (though fully hardcoded).