code: protected static function sortFileList(array $a, array $b)
      {
          if (!array_key_exists("src", $a) || !array_key_exists("src", $b) || !array_key_exists(
                  "type",
                  $a
              ) || !array_key_exists("type", $b)
          ) {
              return 0;
  
              throw new Ts3Exception("invalid parameter", 0x602);
          }
  
          if ($a["type"] != $b["type"]) {
              return ($a["type"] < $b["type"]) ? -1 : 1;
          }
  
          return strcmp(strtolower($a["src"]), strtolower($b["src"]));
      }
docs: Internal callback funtion for sorting of file list items.
  
  @param  array $a
  @param  array $b
  @throws \Teamspeak3\Ts3Exception
  @return integer