 of the <code>data</code> argument.</p></dd>

<dt>id</dt>
<dd><p>a copy of the grouping variable from <code>data</code>.</p></dd>

<dt>id_name</dt>
<dd><p>a character string with the name of the grouping variable.</p></dd>

<dt>Terms</dt>
<dd><p>a list with two terms components, <code>termsX</code> derived from the <code>fixed</code>
    argument, and <code>termsZ</code> derived from the <code>random</code> argument.</p></dd>

<dt>model_frames</dt>
<dd><p>a list with two model.frame components, <code>mfX</c