                       </code>
                              </td>
                              <td>
                                <div>
                                  <p>The parameters of the labels for vertical
                 lines at the top of the grid. If specified <code>nil</code>, no such labels
                 will be drawn. Default value is <code>nil</code>.</p>
                                </div>
                              </td>
                            </tr>
                    