code: func (el *ChannelEventListener) RegAttachingToTangle() *ChannelEventListener {
  	el.AttachingToTangle = make(chan struct{})
  	el.ids = append(el.ids, el.em.RegisterListener(func(data interface{}) {
  		el.AttachingToTangle <- struct{}{}
  	}, event.EventAttachingToTangle))
  	return el
  }
docs: // RegAttachingToTangle registers this listener to listen to when Proof-of-Work is executed.