message: add note to JSON appendix of CmdStan manual
diff: @@ -62,7 +62,7 @@ data {
  \end{Verbatim}
  \end{quote}
  \noindent
  -the following JSON input file would be valid
  +the following JSON input would be valid
  \begin{quote}
  \begin{Verbatim}
  { "d1" : 2,
  @@ -102,6 +102,50 @@ and the right column contains valid JSON data inputs.
  \code{matrix[2,3] a;} & \code{"a" : [ [ 1, 2, 3 ], [ 4, 5, 6] ]} \\
  \end{tabular}
  \end{center}
  +
  +\subsection{Empty arrays in JSON}
  +
  +JSON notation is not able to distinguish between multi-dimensional arrays
  +where any dimension is 0, e.g.,
  +a 2-D array with dimensions (1, 0), i.e., one row, zero columns, has JSON representation \code{ [ ] }.
  +
  +To see how this works, consider the following Stan program data block:
  +\begin{quote}
  +\begin{Verbatim}
  +data {
  + int d;
  + int ar_1d[d];
  + int ar_2d[d,d];
  + int ar_3d[d,d,d];
  +}
  +\end{Verbatim}
  +\end{quote}
  +In the case where variable \code{d} is \code{1}, all arrays will contain 1 value.
  +If where variable \code{ar\_d1} contains value \code{7},
  +variable \code{ar\_d2} contains value \code{8}, and
  +variable \code{ar\_d3} contains value \code{9},
  +the JSON representation is:
  +\begin{quote}
  +\begin{Verbatim}
  +{ "d" : 1,
  + "ar_d1" : [7],
  + "ar_d2" : [[8]],
  + "ar_d3" : [[[9]]]
  +}
  +\end{Verbatim}
  +\end{quote}
  +However, in the case where variable \code{d} is \code{0},
  +all arrays contain 0 values, and the JSON representation is:
  +\begin{quote}
  +\begin{Verbatim}
  +{ "d" : 0,
  + "ar_d1" : [ ],
  + "ar_d2" : [ ],
  + "ar_d3" : [ ]
  +}
  +\end{Verbatim}
  +\end{quote}
  +
  %
  