protected function getCombinedEntries(array $entries)
    {
        $info = $this->concentrator->getCombines(array_keys($entries));

        // add combines to set of entries
        foreach ($info['combines'] as $combine) {
            if (mb_substr($combine, -4) === '.css') {
                $class_name = 'SwatStyleSheetHtmlHeadEntry';
            } elseif (mb_substr($combine, -5) === '.less') {
                $class_name = 'SwatLessStyleSheetHtmlHeadEntry';
            } else {
                $class_name = 'SwatJavaScriptHtmlHeadEntry';
            }
            $entries[$combine] = new $class_name($combine, '__combine__');
        }

        // remove files included in combines
        $entries = array_intersect_key($entries, array_flip($info['files']));

        return array(
            'entries' => $entries,
            'superset' => $info['superset']
        );
    }