/**
   * Adds the CollapsiblePane to the group.
   *
   * @param pane the pane to be added
   */
  public void add(CollapsiblePane pane) {
    if (pane == null) {
      return;
    }
    _panes.add(pane);
    pane.addPropertyChangeListener(CollapsiblePane.EMPHASIZED_PROPERTY, this);

    if (pane.isEmphasized()) {
      if (_selection == null) {
        _selection = pane;
      } else {
        pane.setEmphasized(false);
      }
    }
  }