s and <code>groups</code>
are re-expressed into a form that <code><a href="https://rdrr.io/r/stats/model.frame.html" class="external-link">stats::model.frame()</a></code> can interpret.
Multiple response variables can be separated by <code>+</code> on the left hand side of
the formula.  A one-sided formula <code>~ rhs | cond</code> is treated as <code>rhs ~ 1 | cond</code>.
See details.</p></dd>


<dt>data</dt>
<dd><p>A data frame or list containing the variables.</p></dd>


<dt>...</dt>
<dd><p>Functions us