New York Laws
Part 3 - Varieties of Powers
10-3.4 - Classification of Powers of Appointment as to Duty to Exercise; Imperative and Discretionary

(a) A power of appointment is either imperative or discretionary.
(b) A power of appointment is imperative if the instrument creating it
imposes on the donee a duty to exercise it, and it may be imperative
even though it is exclusive.
(c) A power of appointment is discretionary if the donee is authorized
to exercise or not to exercise it.