public static function setMode($mode = 0, $severity = 1)
 {
     switch ($mode) {
         case self::MODE_OFF:
             self::$trackInput = false;
             self::$trackActivity = false;
             break;
         case self::MODE_LOG_ALL:
             self::$trackInput = true;
             self::$trackActivity = true;
             break;
         case self::MODE_LOG_UNSANITIZED:
             self::$trackInput = true;
             break;
         case self::MODE_LOG_ACTIVITY:
             self::$trackActivity = true;
             break;
     }
     self::$minSeverity = $severity;
 }