code: func (h *BlockHeader) BtcEncode(w io.Writer, pver uint32, enc MessageEncoding) error {
  	return writeBlockHeader(w, pver, h)
  }
docs: // BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
  // This is part of the Message interface implementation.
  // See Serialize for encoding block headers to be stored to disk, such as in a
  // database, as opposed to encoding block headers for the wire.