Sokar Rostau said:
This adds up to 21 possibilities. We actually have here one class of items (mace class) divided into four "runeword item classes" - clubs, hammers, maces and sceptres...
(etc)
It might be useful to have a bit of an explanation of ItemTypes.txt here. This file defines each of the item type codes the game uses. These codes are 4 letters (sometimes 3) that help the game know what an item "is". The complete table is very complicated, with crossovers and multiple parent loops, but if you restrict it to just socketable items, it becomes a simple tree (which I hope I can format correctly) :
Code:
armo weap
/ | \ / | \
/ | \ / | \
shld tors helm orb miss mele
/ | \ / | \ / \ \________________________________
/ | \ / | \ / \ | | | | | | \
shie head ashd / | \ bow xbow spea swor knif axe pole blun h2h
circ phlm pelt | | _________________/ |
| | / | | | |
abow aspe rod mace hamm club h2h2
/ | \
/ | \
scep wand staf
Every socketable base item is defined as being one of these types. Some are just groups, eg nothing is defined directly as a "blun" = Blunt Weapons. But if an item is a hamm it is also a blun and so also a mele and also a weap.
The runewords are also defined as active on one or more of these classes. For example, Ancient's Pledge is defined on shld. That means it works on all subclasses below it too, shie, head and ashd (which are normal shields, necro heads and pally shields respectively). All of the known shield runewords are defined on shld, but if they wanted they could define them only on shie, which would exclude the heads and pally shields. Exile is actually defined on "pala" which doesn't appear here. That is probably a harmless bug on Blizzard's part, it means the runeword would work in any paladin-specific item, not just shields. But, the shields are the only pally item, so it's OK (would be different for amazons, for example). They probably meant to have "ashd" there.
Helms are a little different. Regular helms are defined as "helm", which then includes the more specific circ, phlm and pelt classes. There is no special subclass for regular helms. That means as long as Blizzard stick to their traditional laziness, an runeword that is defined for helms will also be defined for circlets, pelts, and primal helms. However, the runeword file does actually have the scope to exclude up to 3 subclasses. They could define a word as "helm" but exclude "phlm" and "pelt", then it would only work in regular helms and circlets. So you can't be 100% sure, although they have never used these exclude fields before.
The "blun" subclass is the most interesting. Barbarian Mace Mastery is actually really Blunt Item Mastery, because it gives the bonus to all the items in the subclasses of blun. However, there is such a variety of items there that Blizzard does not define any runewords across the whole blun class (except a few that are defined even higher up, for mele or even all of weap). Runewords like Black (club hamm mace) or Heart of the Oak (staf mace) target specific subclasses.
Anyway, my point, and I do have one, is that there is a
lot of flexibility in the runeword definition system. It is very hard to rule out large classes based on one test. Body armour (tors) is about your best bet because it has no subclasses. As are orbs, I suspect, especially since so far they have never added an orb runeword except the ones that work for all of "weap".