The only DR I know of that stacks is X/- from the alternate armor rules, which has explicit exceptions.
Heh, indeed you are right! I was adjudicating it incorrectly all along. Thank you! This is from DMG p 292
DR 5 Cold-Holy on a suit of armour is bypassed by an arrow shot from a Longbow of Frost +2 but DR 5 Holy is not
I am not 100% sure what @Shiningted exactly needs, but if I can help with a generic item condition, I will write one as well. Same pattern as the generic monster Dr, arg 1 value, arg2 Type. Just adding a bonus list instead.
You also need to determine what exactly it's bonusing. In Ted's case I suppose that's a skill, so you'd need a 3rd arg for skill enum. But then you wouldn't be able to squeeze it in protos.tab, since there's only 2 params. You could code it for a particular skill, but then it wouldn't be generic, so you might as well create a custom modifier (which is how it currently is, except the bonus type is baked in). Re. DR stacking: not 100% sure but I think that in ToEE they would stack (bug).
Thanks Sagenlicht. I was thinking of things like Insight Bonus, Luck Bonus (not Poison), Alchemical Bonus - it would be nice to add these in protos.tab. (Its not a priority, I wasn't planning on making anything specific though I would like to do the alchemical stuff properly in time). Just, if you are redoing that part of the game, something to keep in mind. You could still do all the Monster DR boni as a single condition with args. On the other hand, if and when the exact nomenclature is figured out, I'll put my hand up to do these (that is, I'll make a new masterwork proto of every metal weapon then add "Weapon Cold Iron" or whatever it is decided to call it). I'll need a clear proto range in which to stick it. I'll also do the existing Holy Weapons since holy weapons are intended to kill demons so making them out of cold iron seems reasonable. Most magic weapons wouldn't be made from cold iron. I'll do the Frost Brand too - can't detract from a favourite Balor-whacker. Scather and Fragarach will depend on lore, I guess. EDIT: Lore says Fragarach is Steel, btw.
Hmm, about skill bonuses - we could make a generator that pulls the params from a table/json (bonus type, event type, description) and generates them from template.
Why not just, (for instance), "Alchemical Bonus, skill_decipher_script, 1" or "Alchemical Bonus, attribute_charisma, 2" or "Alchemical bonus, saving_throw_fortitude, 1" - new bonus, old args? Mali would presumably then work with negative numbers too.
Related to this topic, does anyone know of official spells that temporarily make a weapon strike as cold iron/silver/adamantine like you can with aligned/magic? It seems like having the party spell casters prepare some of those just in case might be more palatable than the "golf bag" that people complain about. Use teamwork to overcome the problem. I think it's easy enough to implement, but an official spell would mean I don't need to think about what level it should be and so on. Edit: Book of Exalted Deeds has silver and adamantine. I found a suggestion that perhaps it's a specific choice to not allow it for cold iron, but if you have the other two, I guess you can just prefer cold iron as the default anyway.
The Alchemical capsules I added, which are from Complete Adventurer for memory, had a silver option too if I remember correctly: silvers your weapon for the next round. Not really relevant
They were very interesting to try. You can buy them from the alchemist in Verbonc. However, 2 issues made them hard to use: If you put a stack in slot, the entire stack was used at once for a single use effect. This made inventory juggling a real pain. The slot occupied conflicted with many bracers and gloves. More inventory pains. IIRC the effect was only for one attack, not the entire round. So they became much less interesting for higher level characters with more attacks/round.