left unspecified)),
<code>avar</code>,
<code>mvar</code>,
<code>avar:mvar</code> (a zero element is added when <code>interaction = FALSE</code>).
<code>cvar</code> (this part is eliminated when <code>cvar = NULL</code>),
<code>emm_ac_yreg</code> (this part is eliminated when <code>emm_ac_yreg = NULL</code>),
<code>emm_mc_yreg</code> (this part is eliminated when <code>emm_mc_yreg = NULL</code>).</p>
    </div>

    <div id="ref-usage">
    <div class="sourceCode"><pre class="sourceCode r"><code><span class=