Optional /(?)/

Op·tion·al

Optional

a.
  1. Involving an option; depending on the exercise of an option; left to one's discretion or choice; allowed but not compulsory; as, optional studies; it is optional with you to go or stay.
    If to the former the movement was not optional, it was the same that the latter chose when it was optional.
    — Palfrey.
    Original writs are either optional or peremptory.