 with grouped options.
          This widget is functionally similar to an HTML <code>select</code> element with <code>size</code> greater than 1 and options grouped into categories with labeled <code>optgroup</code> elements.
        </p>
        <p>Similar examples include:</p>
        <ul>
          <li><a href="listbox-scrollable.html">Scrollable Listbox Example</a>: Single-select listbox that scrolls to reveal more options, similar to HTML <code>select</code> with <code>size</code> attribute greater th