Complex sentence: The rule against perpetuities at common law invalidates certain future interests (traditionally contingent remainders and executory interests) that may vest beyond the time of perpetuities; the rule "limit (s) the testator's power to earmark gifts for remote descendants".
Split into simpler sentences: The rule against perpetuities at common law invalidates certain future interests (traditionally contingent remainders and executory interests) that may vest beyond the time of perpetuities. In essence, the rule "limit (s) the testator's power to earmark gifts for remote descendants".