A rule that permits consideration of events occurring subsequent to the inception of an instrument that pertains to the vesting of a future interest. If the specified contingency on which the creation of the interest depends actually occurs within the period of the RULE AGAINST PERPETUITIES, the interest is legally enforceable.

Under the COMMON LAW, the Rule Against Perpetuities provides that no interest in property is valid unless it becomes fixed, if at all, not later than twenty-one years, plus the period of gestation, after some life or lives in being at the time of the creation of the interest. The period of gestation is included to cover cases of posthumous birth. A property interest vests when it is given to a person in being, and when the interest is not...