code: func Raw(b []byte) Field {
  	return func(p *Packet) error {
  		if p.Len()+len(b) > MaxEIRPacketLength {
  			return ErrNotFit
  		}
  		p.b = append(p.b, b...)
  		return nil
  	}
  }
docs: // Raw appends the bytes to the current packet.
  // This is helpful for creating new packet from existing packets.