arg--"></a></dt>
<dd><p>Named arguments passed on to <code><a href="p_group_by.html">p_group_by</a></code></p><dl><dt><code>.messages</code></dt>
<dd><p>a set of glue specs. The glue code can use any global
variable, or {.cols} which is the columns that are being grouped by.</p></dd>

<dt><code>.headline</code></dt>
<dd><p>a headline glue spec. The glue code can use any global
variable, or {.cols}.</p></dd>

<dt><code>.tag</code></dt>
<dd><p>if you want the summary data from this step in the future then
giv