  <div class="ref-description section level2">
    <p>This internal utility function extracts key components—such as model frames, matrices,
and response variables—from formulas and a data set. It is used by models like
<code>HeckmanCL</code>, <code>HeckmanGe</code>, <code>HeckmanSK</code>, <code>HeckmanBS</code>, and <code>HeckmantS</code>.
Additionally, it can handle covariate matrices for modeling dispersion (<code>sigma</code>) and
correlation (<code>rho</code>) structures.</p>
    </div>

    <div 