in the "Groups" example, there is an <li/> nested inside an <li/> with no list element in between. is this valid markup?

  <ul class="main">
    <li class="main">
      <details>
        <summary>File</summary>
        <div class="options">
          <fieldset>
            <li class="sub"><a href="/open">Open</a></li>
          </fieldset>
        </div>
      </details>
    </li>
  </ul>

i would think that an <li/> must be the direct child of an ol, ul, or menu.