Stack

Abilities or skills that "stack" are considered additive. For example, modifiers of +1 save all and +2 save against fear "stack" to create a total +3 to save fear (in addition to the +1 to save everyhing else).

Abilities or skills that do not stack will use the modifier that is greater. For example, a +3 and +5 unstackable modifier will apply the +5 to the bonus.