p>
<p>This is similar to grouping by the <code>id_cols</code> then summarizing the
unused columns using <code>unused_fn</code>.</p></dd>


<dt id="arg--messages">.messages<a class="anchor" aria-label="anchor" href="#arg--messages"></a></dt>
<dd><p>a set of glue specs. The glue code can use any global
variable, grouping variable, or {.strata}. Defaults to nothing.</p></dd>


<dt id="arg--headline">.headline<a class="anchor" aria-label="anchor" href="#arg--headline"></a></dt>
<dd><p>a headline glue spec. The 