public function get_last_updated($asstring = false) {
        $data = $this->data;
        $time = null;

        if (isset($data[Parser::INDEX_LISTS_LIST_UPDATED])) {
            $time = $data[Parser::INDEX_LISTS_LIST_UPDATED][0]['value'];
            $time = strtotime($time);
        }

        if ($asstring && $time) {
            return $this->contextual_time($time);
        }

        return $time;
    }