public function output_html($data, $query='') {
        global $OUTPUT;

        $o = '';
        if (!extension_loaded($this->extension)) {
            $warning = $OUTPUT->pix_icon('i/warning', '', '', array('role' => 'presentation')) . ' ' . $this->description;

            $o .= format_admin_setting($this, $this->visiblename, $warning);
        }
        return $o;
    }