Bug 126658 [CommonNavigator] [DND] Complete definition of DND API
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
for (int i = 0; i < descriptors.length; i++) {
				if (isActive(descriptors[i].getId())
						&& isRootExtension(descriptors[i].getId())) {
					extension = getExtension(descriptors[i]);
					if (!extension.hasLoadingFailed())
						rootExtensions.add(extension);
				}
			}
		}
		if (rootExtensions.isEmpty())
			return findContentExtensionsByTriggerPoint(anElement);
		return rootExtensions;
	}
	/**
	 * Search for extensions that declare the given element in their
	 * <b>possibleChildren</b> expression.
	 * 
	 * @param anElement
	 *            The element to use in the query
	 * @return The set of {@link INavigatorContentExtension}s that are
	 *         <i>visible</i> and <i>active</i> for this content service and
	 *         have a <b>possibleChildren</b> expression that is <i>enabled</i>
	 *         for the given element.
	 */
	public Set findOverrideableContentExtensionsForPossibleChild(
			Object anElement) {
		Set overrideableExtensions = new TreeSet(
				ExtensionPriorityComparator.INSTANCE);
		Set descriptors = findDescriptorsWithPossibleChild(anElement);
		for (Iterator iter = descriptors.iterator(); iter.hasNext();) {