Implemented by displays that can be given accept an {@link IsWidget} to show.

abstract class AcceptsOneWidget {

 /**
  * Set the only widget of the receiver, replacing the previous
  * widget if there was one.
  *
  * @param w the widget, or <code>null</code> to remove the widget
  *
  * @see SimplePanel
  */
 void setWidgetIsWidget(IsWidget w);
}