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/filebuffers/CompilationUnitDocumentProvider2.java
annotation.setOverlay(null);
					}
				}			
			}
			
			/**
			 * Overlays value with problem annotation.
			 * @param problemAnnotation
			 */
			private void setOverlay(Object value, ProblemAnnotation problemAnnotation) {
				if (value instanceof  JavaMarkerAnnotation) {
					JavaMarkerAnnotation annotation= (JavaMarkerAnnotation) value;
					if (annotation.isProblem()) {
						annotation.setOverlay(problemAnnotation);
						fPreviouslyOverlaid.remove(annotation);
						fCurrentlyOverlaid.add(annotation);
					}
				}
			}
			
			private void  overlayMarkers(Position position, ProblemAnnotation problemAnnotation) {
				Object value= getAnnotations(position);
				if (value instanceof List) {
					List list= (List) value;
					for (Iterator e = list.iterator(); e.hasNext();)
						setOverlay(e.next(), problemAnnotation);
				} else {
					setOverlay(value, problemAnnotation);
				}
			}