code: function addChangeEvent(eventName, target){
              var fnName = eventName.charAt(0).toUpperCase() + eventName.substring(1);
              var event = {};
              event['on' + fnName] = createEventSubscriptionFn(eventName);
              event['publish' + fnName] = createPublishEventFn(eventName);
              return angular.extend(target, event);
          }
docs: ////////