public static function stylesToProc($files = array())
    {
        if (!class_exists('XsltProcessor')) {
            throw new BadMethodCallException('XSL extension is missing. Can not create XsltProcessor.');
        }

        $dom = self::stylesToDOM($files);
        $proc = new XsltProcessor();
        $proc->importStylesheet($dom);

        return $proc;
    }