docs: public void addFile(String url) {
          int count = windowMenu.getItemCount();
          JMenuItem item;
          if (count == 4) {
              windowMenu.addSeparator();
              count++;
          }
          JMenuItem lastItem = windowMenu.getItem(count -1);
          boolean hasMoreWin = false;
          int maxWin = 5;
          if (lastItem != null &&
             lastItem.getText().equals("More Windows...")) {
              hasMoreWin = true;
              maxWin++;
          }
          if (!hasMoreWin && count - 4 == 5) {
              windowMenu.add(item = new JMenuItem("More Windows...", 'M'));
              item.setActionCommand("More Windows...");
              item.addActionListener(this);
              return;
          } else if (count - 4 <= maxWin) {
              if (hasMoreWin) {
                  count--;
                  windowMenu.remove(lastItem);
              }
              String shortName = SwingGui.getShortName(url);
  
              windowMenu.add(item = new JMenuItem((char)('0' + (count-4)) + " " + shortName, '0' + (count - 4)));
              if (hasMoreWin) {
                  windowMenu.add(lastItem);
              }
          } else {
              return;
          }
          item.setActionCommand(url);
          item.addActionListener(this);
      }