private function get_list_or_item($data, $field, $i = null, $default = '')
    {
        $i = ($i === false || count($this->article_ids) > 1 ) ? $i : 0;

        if ($i === null || $i === false) {
            $result = [];
            foreach ($data as $page_id => $item) {
                $result[$page_id] = isset($item[$field]) ? $item[$field] : $default;
            }
            return $result;
        }

        return isset($data[$this->article_ids[$i]][$field]) ? $data[$this->article_ids[$i]][$field] : $default;
    }