protected function _setStylesheet($href, $media = null, $prepend = false, $conditional = '')
    {
        //obliczanie timestampa
        $ts = $this->_getLocationTimestamp($href);
        //określanie parametrów
        $params = ['rel' => 'stylesheet', 'type' => 'text/css', 'href' => $ts > 0 ? $this->_getPublicSrc($href) : $href, 'ts' => $ts];
        if ($media) {
            $params['media'] = $media;
        }
        return $this->headLink($params, $prepend, $conditional);
    }