@Override
  protected JPanel appendCheckboxes(ItemListener itemListener) {
    final JPanel panel = new JPanel(new GridBagLayout());
    appendOccurrences(itemListener, new GridBagConstraints(0, 0, 1, 1, 0, 0, GridBagConstraints.NORTHWEST, GridBagConstraints.NONE,
                                                           JBInsets.emptyInsets(), 0, 0), panel);
    return panel;
  }
@Override
  protected JPanel appendCheckboxes(ItemListener itemListener)