code: func NewRegistrar(ledgerFactory blockledger.Factory,
  	signer crypto.LocalSigner, metricsProvider metrics.Provider, callbacks ...channelconfig.BundleActor) *Registrar {
  	r := &Registrar{
  		chains:             make(map[string]*ChainSupport),
  		ledgerFactory:      ledgerFactory,
  		signer:             signer,
  		blockcutterMetrics: blockcutter.NewMetrics(metricsProvider),
  		callbacks:          callbacks,
  	}
  
  	return r
  }
docs: // NewRegistrar produces an instance of a *Registrar.