code: func (s *SystemChannel) ProcessNormalMsg(msg *cb.Envelope) (configSeq uint64, err error) {
  	channelID, err := utils.ChannelID(msg)
  	if err != nil {
  		return 0, err
  	}
  
  	// For the StandardChannel message processing, we would not check the channel ID,
  	// because the message processor is looked up by channel ID.
  	// However, the system channel message processor is the catch all for messages
  	// which do not correspond to an extant channel, so we must check it here.
  	if channelID != s.support.ChainID() {
  		return 0, ErrChannelDoesNotExist
  	}
  
  	return s.StandardChannel.ProcessNormalMsg(msg)
  }
docs: // ProcessNormalMsg handles normal messages, rejecting them if they are not bound for the system channel ID
  // with ErrChannelDoesNotExist.