>> The only exception to similar types stacking is "Circumstantial"
> Nope "Dodge" stacks with itself as well.
>> Natural Armor from any sorce only grants the better One Sorce. Be
>> it Natural or otherwise. Just like Deflection bonuses. Only one
>> will work, and usually the best one any single PC has at the time.
> Right but the Amulet of Natural Armor does not grant a "Natural Armor
> bonus to AC" it grants "an enhancement bonus to his natural armor
> bonus" and I think this should be a new type.
Not really a new type. You can have multpile enhancement bonuses in
effect, just not on the same thing. E.g. up to +5 to your dex, +5 to a
shield and a suit of armor (+10 total for those) and +5 on your natural
armor (normally +0 for core races). This would give a pretty hefty
boost to the AC of the character (17.5 total boost) that all, in
essence, stack, but are enhancements to different things.
The rest becomes programming conventions and not in game term
conventions for needs of stacking all these various bonuses. Could just
leave them all as type=enhancement and then use something else to define
the base that they are enhancing. (attribute, armor, shield, natural
armor). So... maybe something like