public function writeMinified($mask = '%s')
    {
        $str='';
        foreach ($this->cleanStack($this->getMinified(), 'file') as $entry) {
            $tag_attrs = array(
                'rel'=>'stylesheet',
                'type'=>'text/css',
                'href'=>$entry['file']
            );
            if (isset($entry['media']) && !empty($entry['media']) && $entry['media']!='screen') {
                $tag_attrs['media'] = $entry['media'];
            }
            $str .= sprintf($mask, Html::writeHtmlTag('link', null, $tag_attrs, true));
        }
        return $str;
    }