optional; non-mandatory(~ audit – дополнительная / внеочередная аудиторская проверка, проведение которой компания заказывает, напр., чтобы предоставить дополнительное подтверждение своей надежности Alexander Oshis)
voluntarily(I offer my waiver of jury trial freely and voluntarily with full understanding of all matters set forth in the indictment and in this petition. — Я добровольно и без принуждения подаю отказ от суда присяжных, полностью понимая все факты, которые изложены в официальном обвинительном акте и в настоящем заявлении.)
of one's own will("The owner of an open-top convertible called Vancouver police about 6 p.m. on Sunday to say he had returned to his parked Chevrolet Corvette supercar in the Sunset Beach parking lot to find a stranger had climbed inside the vehicle through the open roof and was sitting in the driver's seat without his consent. (...) When it became clear the man would not leave the car of his own will, officers used a bean bag shotgun on the man's legs, which allowed officers to move in and arrest the 36-year-old Vancouver man." (The Province)ART Vancouver)
