public function extractFiles($outputFolder, $files = null, $expandFilesList = false)
    {
        if ($files !== null) {
            if (is_string($files)) $files = [$files];

            if ($expandFilesList)
                $files = self::expandFileList($this->files, $files);

            return $this->archive->extractFiles($outputFolder, $files);
        } else {
            return $this->archive->extractArchive($outputFolder);
        }
    }