public function removeExcludeDay($day)
 {
     if (!is_int($day) || $day < 1 || $day > 31) {
         throw new \DomainException("You must describe days of the month using integers between 1 and 31");
     } else {
         parent::removeExcludeDay($day);
     }
 }
 public function jsonSerialize()
 {
     $pre = parent::jsonSerialize();
     if (!empty($pre->excludeDaysFlags)) {
         $pre->excludeDaysFlags = array("excludeDayFlag" => $this->generateFlagArray());
     }
     return $pre;
 }