code: func (z *Dec) QuoExact(x, y *Dec) *Dec {
  	return z.quo(x, y, scaleQuoExact{}, RoundExact)
  }
docs: // QuoExact sets z to the quotient x/y and returns z when x/y is a finite
  // decimal. Otherwise it returns nil and the value of z is undefined.
  //
  // The scale of a non-nil result is "x.Scale() - y.Scale()" or greater; it is
  // calculated so that the remainder will be zero whenever x/y is a finite
  // decimal.