code: func (msg *MsgHeaders) AddBlockHeader(bh *BlockHeader) error {
  	if len(msg.Headers)+1 > MaxBlockHeadersPerMsg {
  		str := fmt.Sprintf("too many block headers in message [max %v]",
  			MaxBlockHeadersPerMsg)
  		return messageError("MsgHeaders.AddBlockHeader", str)
  	}
  
  	msg.Headers = append(msg.Headers, bh)
  	return nil
  }
docs: // AddBlockHeader adds a new block header to the message.