code: func (b *Bytes) UnmarshalText(input []byte) error {
  	raw, err := checkText(input, true)
  	if err != nil {
  		return err
  	}
  	dec := make([]byte, len(raw)/2)
  	if _, err = hex.Decode(dec, raw); err != nil {
  		err = mapError(err)
  	} else {
  		*b = dec
  	}
  	return err
  }
docs: // UnmarshalText implements encoding.TextUnmarshaler.