hich contains a single array which is empty,
has JSON representation <code>[ ]</code>.
To see how this works, consider the following Stan program data block:</p>
<pre><code>data {
  int d;
  int ar_1d[d];
  int ar_2d[d,d];
  int ar_3d[d,d,d];
}</code></pre>
<p>In the case where variable <code>d</code> is <code>1</code>, all arrays will contain a single value.
If array variable <code>ar_d1</code> contains value <code>7</code>,
2-D array variable <code>ar_d2</code> contains (an array which contains) value <co