Persons benefited by a will need not be in existence at the time of such will, nor be absolutely described or identified therein. It is sufficient that at the time of the death of the testator they be in existence, or that they be then conceived and subsequently born viable, and be clearly known to be the persons intended by the testator. Even in the case of suspended legacies, already referred to in this article, it suffices that the legatee be alive, or conceived, subject to the condition of being afterwards born viable, and proving to be the person indicated, at the time the legacy takes effect in his favour.