e>) and groups are configured to be reorderable (via <code>groupEditable.order</code>), the user has to provide a function that swaps the positions of two given groups.
      If this option is not set, the default implementation assumes that groups hold an attribute <code>order</code> which values are changed. The signature of the <code>groupOrderWap</code> function is:
      <pre class="prettyprint lang-js">function groupOrderSwap(fromGroup: Object, toGroup: Object, groups: DataSet)</pre>
      The first t