Membership of class; determination; after born members.

Sec. 21. Except as provided in section 20, when the donee of a power executes an instrument exercising the power in favor of a class, the membership of the class shall be determined as of the effective date of the exercise and include any person otherwise qualified as a member of the class who was born after the execution of the instrument exercising the power and before the effective date of the exercise unless a different intention is apparent from the instrument exercising the power.