code: func (d *Decoder) iDnSize() ([4]byte, uint32, error) {
  	var ID [4]byte
  	var blockSize uint32
  	if d.err = binary.Read(d.r, binary.BigEndian, &ID); d.err != nil {
  		return ID, blockSize, d.err
  	}
  	if d.err = binary.Read(d.r, binary.BigEndian, &blockSize); d.err != nil {
  		return ID, blockSize, d.err
  	}
  	return ID, blockSize, nil
  }
docs: // iDnSize returns the next ID + block size