code: public static function setExcelCalendar($baseDate)
      {
          if (($baseDate == self::CALENDAR_WINDOWS_1900) ||
              ($baseDate == self::CALENDAR_MAC_1904)) {
              self::$excelCalendar = $baseDate;
  
              return true;
          }
  
          return false;
      }
docs: Set the Excel calendar (Windows 1900 or Mac 1904).
  
  @param int $baseDate Excel base date (1900 or 1904)
  
  @return bool Success or failure