/** grouping PKCS7-[XXX]-[XXX] files */
  private boolean _addGroup() {
    String strMethod = "_addGroup()";

    // adding radioButtons/labelChecks for selecting in between JAR, and JHR, and RCR files

    if (this._btnTypeFileShkDer == null) {
      MySystem.s_printOutError(this, strMethod, "nil this._btnTypeFileShk[xxx]");
      return false;
    }

    // ----

    ButtonGroup bgp = new ButtonGroup();
    // bgp.add(this._btnTypeFileShkPkcs7);

    if (this._btnTypeFileShkPem != null) bgp.add(this._btnTypeFileShkPem);

    bgp.add(this._btnTypeFileShkDer);

    if (bgp.getButtonCount() < 2) {
      this._btnTypeFileShkDer.setEnabled(false);
    }

    // selecting first button
    this._btnTypeFileShkDer.setSelected(true);

    // else label: done at construction time

    // --
    JPanel pnlTypeFileShk = new JPanel();
    pnlTypeFileShk.setLayout(new BoxLayout(pnlTypeFileShk, BoxLayout.Y_AXIS));
    pnlTypeFileShk.add(this._btnTypeFileShkDer); // default

    if (this._btnTypeFileShkPem != null) pnlTypeFileShk.add(this._btnTypeFileShkPem);

    // --
    if (super._pnl_ == null) {
      MySystem.s_printOutError(this, strMethod, "nil super._pnl_");
      return false;
    }

    super._pnl_.add(pnlTypeFileShk);

    // ending
    return true;
  }