>> assignments from exams, however, the use of a full nested list was
 >> inappropriate, since nested lists would produce a sub-menu style,

 > Only with an inappropriate style sheet.

Would this be possible even if some times a sub menu was required and 
othertime, just a grouped set?

for example:
<nl>
    <label>NavMenu</label>
    <ligroup>
        <label>Group 1</label>
        <li>NavMenu item1</li>
        <nl>
            <label>SubMenu</label>
            <li>SubMenu Item1</li>
        </nl>
    </ligroup>
    <ligroup>
        <li>NavMenu item2</li>
        <li>NavMenu item3</li>
    </ligroup>
</nl>

so this should render like:
NavMenu
  ___Group 1___
  NavMenu Item1
  SubMenu     > SubMenu Item1
  ___Group 2___ SubMenu Item2
  NavMenu Item2
  NavMenu Item3

could this be done properly using CSS and Class selectors like this?
<nl>
    <label>NavMenu</label>
    <nl class="ligroup">
        <label>Group 1</label>
        <li>NavMenu item1</li>
        <nl class="submenu">
            <label>SubMenu</label>
            <li>SubMenu Item1</li>
        </nl>
    </nl>
    <nl class="ligroup">
        <label>Group 2</label>
        <li>NavMenu item2</li>
        <li>NavMenu item3</li>
    </nl>
</nl>
If so, great!

CYA
...Lachy