Bug 214649 [Markers] Allow markerAttributeGroupings and markerGroups to be specified within contentGenerators
With everything at the top level it is hard to see the relation to a contentGenerator and the groups and attribute groupings. These should be sub elements a la menus.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/MarkerContentGenerator.java
* @param returnMarkers
	 */
	private void findIntersection(Collection matching, Collection returnMarkers) {
		HashSet removeMarkers = new HashSet();
		Iterator existing = returnMarkers.iterator();
		while (existing.hasNext()) {
			Object next = existing.next();
			if (matching.contains(next))
				continue;
			removeMarkers.add(next);
		}
		returnMarkers.removeAll(removeMarkers);
	}
	/**
	 * Adds all markers in the given set of resources to the given list
	 * 
	 * @param results
	 *            The Collection to add new entries to
	 * @param resources
	 * @param group
	 *            the group to filter on. May be <code>null</code>.
	 * @param depth
	 * @param monitor
	 */
	private void findMarkers(Collection results, IResource[] resources,
			MarkerFieldFilterGroup group, int depth, IProgressMonitor monitor) {
		if (resources == null) {
			return;
		}