docs: private RadioButton addKeyRadioButton(final Grid grid,
                                          final int row, final int col,
                                          final String pos) {
      final RadioButton rb = new RadioButton("keypos");
      rb.addClickHandler(new ClickHandler() {
        public void onClick(final ClickEvent event) {
          keypos = pos;
        }
      });
      rb.addClickHandler(refreshgraph);
      grid.setWidget(row, col, rb);
      keypos_map.put(pos, rb);
      return rb;
    }