code: private boolean addSingle(T element, Class<?> accessibleClass) {
  		List<T> elements = this.elementsForClass.get(accessibleClass);
  
  		if (elements == null) {
  			elements = new ArrayList<T>();
  			this.elementsForClass.put(accessibleClass, elements);
  		}
  
  		if (!elements.contains(element)) {
  			elements.add(element);
  			return true;
  		}
  		return false;
  	}
docs: //////////////