Bug 126658 [CommonNavigator] [DND] Complete definition of DND API
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonViewer.java
public boolean isExpandable(Object element) {
		return getFilteredChildren(element).length != 0;
	}
	/**
	 * <p>
	 * Disposes of the NavigatorContentService, which will dispose the Content
	 * and Label providers.
	 * </p>
	 */
	public void dispose() {
		if (contentService != null)
			contentService.dispose();
	}
	/**
	 * Sets this viewer's sorter and triggers refiltering and resorting of this
	 * viewer's element. Passing <code>null</code> turns sorting off.
	 * 
	 * @param sorter
	 *            a viewer sorter, or <code>null</code> if none
	 */
	public void setSorter(ViewerSorter sorter) {
		if (sorter != null && sorter instanceof CommonViewerSorter)
			((CommonViewerSorter) sorter).setContentService(contentService);
		if (sorter == null || sorter instanceof TreeViewerSorter)
			super.setSorter(sorter);
		else
			/*
			 * we wrap the sorter for convenience (now we can always cast to
			 * TreeViewerSorter)
			 */