* mouse from over a resource item with popup to over a resource set and
* the popup removes the resource a bit later.
*/
highlightedSingleResources = new CountingResourceSet();
combinedHighlightedResources = new UnionResourceSet(
new DefaultResourceSet());
combinedHighlightedResources
.addResourceSet(highlightedResourceSetContainer);
combinedHighlightedResources.addResourceSet(highlightedSingleResources);
}