code: func (el *CallbackEventListener) RegConfirmedTransfers(f BundleEventCallback) {
  	el.ids = append(el.ids, el.em.RegisterListener(func(data interface{}) {
  		f(data.(bundle.Bundle))
  	}, poller.EventTransferConfirmed))
  }
docs: // RegConfirmedTransfers registers the given callback to execute when a transfer got confirmed.