code: func (d *Dialer) subDialerForAddr(raddr ma.Multiaddr) transport.Dialer {
  	for _, pd := range d.Dialers {
  		if pd.Matches(raddr) {
  			return pd
  		}
  	}
  
  	if d.fallback.Matches(raddr) {
  		return d.fallback
  	}
  
  	return nil
  }
docs: // returns dialer that can dial the given address