“The doctrine of independent significance is universally accepted. Under the doctrine, a provision may validly refer to an external circumstance having significance apart from its effect upon the will. The term ‘external circumstance’ includes any fact, act, or event existing or occurring outside of the four corners of the will. An external circumstance has independent significance if it is one that would naturally occur or be done for some reason other than the effect it would have on the testamentary disposition…The rationale for the doctrine is that the independent significance of the external circumstance – its lifetime or non-testamentary character – substitutes for attestation even though the circumstance itself is not attested.” Restatement (Third) of Prop.: Donative Transfers § 3.7 cmt. The Restatement illustrates this point with examples of a bequest of “the car I will own at my death,” a bequest of “the balance on hand in my checking account at my death,” a bequest of “the contents of my safe deposit box.”