code: func (msg *MsgMerkleBlock) AddTxHash(hash *chainhash.Hash) error {
  	if len(msg.Hashes)+1 > maxTxPerBlock {
  		str := fmt.Sprintf("too many tx hashes for message [max %v]",
  			maxTxPerBlock)
  		return messageError("MsgMerkleBlock.AddTxHash", str)
  	}
  
  	msg.Hashes = append(msg.Hashes, hash)
  	return nil
  }
docs: // AddTxHash adds a new transaction hash to the message.