PHB2 P221:
EXTRA DAMAGE
Many effects grant you the ability to deal extra damage, including powers, feats, and magic item properties.
Extra damage is always in addition to other damage. For example, if you have a feat that causes your area attacks to deal extra damage, the extra damage doesn’t apply when you use an area attack that deals no damage, such as the wizard’s sleep power.
framework上的支持暂时就找到这么点...