Bug 258810 [Markers] Markers for the entire workspace show up when working set empty
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/MarkerContentGenerator.java
*            Collection of {@link IMarker}
	 * @param group
	 * @param markers
	 */
	private void filterMarkers(Collection results,
			MarkerFieldFilterGroup group, IMarker[] markers) {
		for (int idx = 0; idx < markers.length; idx++) {
			IMarker marker = markers[idx];
			if (group == null || group.select(marker))
				results.add(marker);
		}
	}
	/**
	 * Iterate through the return markers. If they do not exist in matching
	 * remove them.
	 * 
	 * @param matching
	 * @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);
	}