Modifier

A modifier is any bonus or penalty applying to a die roll. A positive modifier is a bonus, and a negative modifier is a penalty.

Modifiers from the same source do not stack, and modifiers with specific descriptors generally do not stack with others of the same type. If more than one modifier of a type is present, only the best bonus or worst penalty in that grouping applies. Bonuses or penalties that do not have descriptors stack with those that do.