code: func spentTxOutHeaderCode(stxo *SpentTxOut) uint64 {
  	// As described in the serialization format comments, the header code
  	// encodes the height shifted over one bit and the coinbase flag in the
  	// lowest bit.
  	headerCode := uint64(stxo.Height) << 1
  	if stxo.IsCoinBase {
  		headerCode |= 0x01
  	}
  
  	return headerCode
  }
docs: // spentTxOutHeaderCode returns the calculated header code to be used when
  // serializing the provided stxo entry.