1. A testator, settlor, or possessor of any appropriate power of appointment may direct how the estate tax shall be apportioned or allocated or grant a discretionary power to another so to direct. Any such direction shall take precedence insofar as the direction provides for the payment of the estate tax or any part thereof from property the disposition of which can be controlled by the instrument containing the direction or delegating the power to another.
2. Any direction as to apportionment or nonapportionment of the tax, whether contained in a will or in a nontestamentary instrument, shall be limited in its operation to the property passing thereunder unless such will or instrument otherwise directs.