code: func (s *Swarm) RegisterPssProtocol(topic *pss.Topic, spec *protocols.Spec, targetprotocol *p2p.Protocol, options *pss.ProtocolParams) (*pss.Protocol, error) {
  	return pss.RegisterProtocol(s.ps, topic, spec, targetprotocol, options)
  }
docs: // RegisterPssProtocol adds a devp2p protocol to the swarm node's Pss instance