Combines the elements returned by the nested DataProviders Data Providers under a single (new) root element.
The resulting XML can be used directly in a datacontrol, but it is also likely that this UnionFilter is wrapped by a XSLTransformFilter to somehow merge/combine the nested elements.
This UnionFilter requires two parameters in the DataControls.dcx; root-element and root-namespace specifying the element name and namespace.
With the root-element parameter set to foo, the root-namespace parameter set to bar and the two nested DataFilters returning the elements <baz/> & <qux/>, this UnionFilter would return:
...