Bug 40785 [plan item] Overview ruler improvements
- navigation from ruler to editor - hovering over header area shows number of errors/warning (header annotations in general)
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitDocumentProvider.java
*/
			public boolean isRelevant() {
				return true;
			}
			
			/*
			 * @see IJavaAnnotation#hasOverlay()
			 */
			public boolean hasOverlay() {
				return false;
			}
			
			/*
			 * @see IJavaAnnotation#addOverlaid(IJavaAnnotation)
			 */
			public void addOverlaid(IJavaAnnotation annotation) {
				if (fOverlaids == null)
					fOverlaids= new ArrayList(1);
				fOverlaids.add(annotation);
			}
			/*
			 * @see IJavaAnnotation#removeOverlaid(IJavaAnnotation)
			 */
			public void removeOverlaid(IJavaAnnotation annotation) {
				if (fOverlaids != null) {
					fOverlaids.remove(annotation);
					if (fOverlaids.size() == 0)
						fOverlaids= null;
				}
			}