public static function logs($reference = null, $index = 0)
    {
        if (!func_num_args()) {
            return static::$_logs;
        }
        $result = [];
        $count = count(static::$_logs);
        for ($i = $index; $i < $count; $i++) {
            $logs = static::$_logs[$i];
            if ($log = static::_matchReference($reference, $logs)) {
                $result[] = $log;
            }
        }
        return $result;
    }