Bug 302791 [CommonNavigator] Associated editor does not close when deleting resource (editorInput) through CommonNavigator
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/extensions/NavigatorContentDescriptor.java
if(aSelection.isEmpty()) {
			return false;
		}
		for (Iterator iter = aSelection.iterator(); iter.hasNext();) {
			Object element = iter.next();
			if(!isPossibleChild(element)) {
				return false;
			}
		}
		return true;
	}
	/**
	 * 
	 * Does not force the creation of the set of overriding extensions.
	 * 
	 * @return True if this extension has overriding extensions.
	 */
	public boolean hasOverridingExtensions() {
		return overridingExtensions != null && overridingExtensions.size() > 0;
	}
	/**
	 * @return The set of overriding extensions (of type
	 *         {@link INavigatorContentDescriptor}
	 */
	public Set getOverriddingExtensions() {
		if (overridingExtensions == null) {
			overridingExtensions = new TreeSet(ExtensionSequenceNumberComparator.DESCENDING);
		}
		return overridingExtensions;
	}