Resolve conflicts in the specification of memo fields by deferring to…

… ZIP 302.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

protocol/protocol.tex

@@ -8017,24 +8017,22 @@
 
 \introlist
 The usage of the \memo is by agreement between the sender and recipient of the
-\note. The \memo{} \SHOULD be encoded either as:
+\note. The \memo{} \SHOULD be encoded as one of:
 
 \begin{itemize}
   \item a UTF-8 human-readable string \cite{Unicode}, padded by appending zero bytes; or
-  \item an arbitrary sequence of $\MemoByteLength$ bytes starting with a byte value of $\hexint{F5}$
-        or greater, which is therefore not a valid UTF-8 string.
+  \item the byte $\hexint{F6}$ followed by $511$ $\hexint{00}$ bytes, indicating ``no memo''; or
+  \item any other sequence of $\MemoByteLength$ bytes starting with a byte value $\hexint{F5}$
+        or greater (which is therefore not a valid UTF-8 string), as specified in \cite{ZIP-302}.
 \end{itemize}
 
-In the former case, wallet software is expected to strip any trailing zero bytes
-and then display the resulting \mbox{UTF-8} string to the recipient user, where applicable.
-Incorrect UTF-8-encoded byte sequences \SHOULD be displayed as replacement characters
-(\ReplacementCharacter).
+When the first byte value is less than $\hexint{F5}$, wallet software is expected to strip any
+trailing zero bytes and then display the resulting \mbox{UTF-8} string to the recipient user,
+where applicable. Incorrect UTF-8-encoded byte sequences \SHOULD be displayed as replacement
+characters (\ReplacementCharacter).
 
-In the latter case, the contents of the \memo{} \SHOULDNOT be displayed. A start byte
-of $\hexint{F5}$ is reserved for use by automated software by private agreement.
-A start byte of $\hexint{F6}$ followed by $511$ $\hexint{00}$ bytes means ``no memo''.
-A start byte of $\hexint{F6}$ followed by anything else, or a start byte of $\hexint{F7}$
-or greater, are reserved for use in future \Zcash protocol extensions.
+In other cases, the contents of the \memo{} \SHOULDNOT be displayed unless otherwise specified
+by \cite{ZIP-302}.
 }
 
 Other fields are as defined in \crossref{notes}.
@@ -10262,6 +10260,13 @@
 \intropart
 \lsection{Change History}{changehistory}
 
+\historyentry{2020.1.1}{2020-02-13}
+
+\begin{itemize}
+    \item Resolve conflicts in the specification of \memos by deferring to \cite{ZIP-302}.
+\end{itemize}
+
+
 \historyentry{2020.1.0}{2020-02-06}
 
 \begin{itemize}

protocol/zcash.bib

@@ -920,6 +920,15 @@ @misc{ZIP-243
    urldate={2019-08-28}
 }
 
+@misc{ZIP-302,
+   presort={ZIP-0302},
+   author={Jay Graber and Jack Grigg},
+   title={Standardized Memo Field Format},
+   howpublished={Zcash Improvement Proposal 302 (in progress).},
+   url={https://github.com/zcash/zips/pull/105},
+   urldate={2020-02-13}
+}
+
 @misc{DigiByte-PoW,
    presort={DigiByte-PoW},
    author={DigiByte Core Developers},