subgroups by a field name or custom sort function.
        By default, groups are ordered by first-come, first-show.
      </td>
    </tr>
    <tr>
      <td>subgroupStack</td>
      <td>Object or Boolean</td>
      <td>none</td>
      <td>Enables stacking within individual subgroups. Example: <code>{'subgroup0': true, 'subgroup1': false, 'subgroup2': true}</code> 
          For each subgroup where stacking is enabled, items will be stacked on top of each other within that subgroup such that they do no over