code: func (u *UUID) UnmarshalBinary(data []byte) (err error) {
  	if len(data) != Size {
  		err = fmt.Errorf("uuid: UUID must be exactly 16 bytes long, got %d bytes", len(data))
  		return
  	}
  	copy(u[:], data)
  
  	return
  }
docs: // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
  // It will return error if the slice isn't 16 bytes long.