code: public function attach(EventManagerInterface $events, $priority = 1)
      {
          foreach ($this->listenerSpecs as $name => $spec) {
              $this->listeners[] = $events->attach($spec['event'], array($this, "do$name"), $spec['priority']);
          }
      }
docs: Attachs listener creation and invokation callback.
  
  For each specification this aggregate attachs itself to the event manager on the
  specified event to be able to react upon triggering.
  
  @param EventManagerInterface $events
  
  @return void