code: public void addListener(IProblemChangedListener listener) {
  		if (fListeners.isEmpty()) {
  			VdmUIPlugin.getWorkspace().addResourceChangeListener(this);
  			//VdmUIPlugin.getDefault().getCompilationUnitDocumentProvider().addGlobalAnnotationModelListener(this);
  		}
  		fListeners.add(listener);
  	}
docs: Adds a listener for problem marker changes.
  @param listener the listener to add