public static function getSymbol($type = self::SYMBOL_LOWER)
	{
		switch ($type) {
			case self::SYMBOL_LOWER:
				return chr(mt_rand(97, 122));
				break;
			case self::SYMBOL_UPPER:
				return chr(mt_rand(65, 90));
				break;
			case self::SYMBOL_DIGIT:
				return mt_rand(0, 9);
				break;
			default:
				return null;
		}
	}