code: func checkSerializedHeight(coinbaseTx *btcutil.Tx, wantHeight int32) error {
  	serializedHeight, err := ExtractCoinbaseHeight(coinbaseTx)
  	if err != nil {
  		return err
  	}
  
  	if serializedHeight != wantHeight {
  		str := fmt.Sprintf("the coinbase signature script serialized "+
  			"block height is %d when %d was expected",
  			serializedHeight, wantHeight)
  		return ruleError(ErrBadCoinbaseHeight, str)
  	}
  	return nil
  }
docs: // checkSerializedHeight checks if the signature script in the passed
  // transaction starts with the serialized block height of wantHeight.