A <ul> element must appear within an <li> element, not another <ul> element.

https://download.java.net/java/early_access/javafx26/docs/api/javafx.graphics/javafx/scene/doc-files/cssref.html

For example, in jfx.incubator.scene.control.richtext.RichTextArea, the Substrcture subtopic, the nested unonrdered list is not structured correctly:

    <ul>
      <li>main-pane — Pane</li>
        <ul>
          <li>vflow — Pane</li>
          <ul>
            <li>content — Pane</li>
            <ul>
              <li>caret-line — Path</li>
              <li>selection-highlight — Path</li>
              <li>flow — Pane</li>
              <li>caret — Path</li>
            </ul>
            <li>left-side — Pane</li>
            <li>right-side — Pane</li>
          </ul>
          <li>scroll-bar:vertical — ScrollBar</li>
          <li>scroll-bar:horizontal — ScrollBar</li>
        </ul>

It should be like this:

    <ul>
      <li>main-pane — Pane
        <ul>
          <li>vflow — Pane
            <ul>
              <li>content — Pane
                <ul>
                  <li>caret-line — Path</li>
                  <li>selection-highlight — Path</li>
                  <li>flow — Pane</li>
                  <li>caret — Path</li>
                </ul>
              </li>
              <li>left-side — Pane</li>
              <li>right-side — Pane</li>
            </ul>
          </li>
          <li>scroll-bar:vertical — ScrollBar</li>
          <li>scroll-bar:horizontal — ScrollBar</li>
        </ul>
      </li>
    </ul>

An aside: The em dash character (—) should be replaced with the &mdash; HTML entity.

    </ul>

See 1.3.1 Info and Relationships in OAG 3.2.