* a gripping area or header label.
*/
public void setWidgets(List<T> widgets, Function<T, Widget> getDragTarget) {
AbsolutePanel boundaryPanel = new AbsolutePanel();
boundaryPanel.setSize("100%", "100%");
boundaryPanel.clear();
content.clear();
content.add(boundaryPanel);
// The VerticalPanel which actually holds the list of widgets.