Courseware material authoring customization layer (Was: Recusive<section/>'s and their conclusions)

The matter of my question is that i'm working on customization layer for courseware 
material authoring.

Now I use following style for the (self assesment) labs markup:

<article role="labkit" lang="ru"
	 xmlns="http://docbook.org/docbook-ng">
   <info>
     <title>Course Name</title>
     <authorgroup>
	...
     </authorgroup>
   </info>

   <section role="lab" >
     <title>Lab title</title>

     <highlights role="tasks">
	<!-- Lab tasks explanation -->
     </highlights>

     <highlights role="objectives">
	<!-- Lab objectives explanation -->
     </highlights>

     <section role="topic">
       <title>Topic title</title>

        <section role="topic">
          <title>Subtopic title</title>

          <!-- Topic matter -->
        </section>

        <section role="exercise">
          <title>Exercise title</title>

          <!-- Exercise matter -->
        </section>
     </section>

<!-- Here I want to conclude lab: quiz, etc... -->

   </section>
</section>

but due to current DTD and DocBook NG schema it's not possible to use something "more 
semantic" (e.g <highlights/>) than section to conclude.

Any thoughts?