docs: public void add(HelpTopic topic) {
          if (topic != null && topic.getURL() != null && !sameTopic(topic, getCurrentItem())) {
              removeRange(position + 1, history.size());
              removeRange(0, history.size() - maxsize);
              position = history.size();
              history.add(topic);
          }
  
          notifyListeners(topic);
      }