Grouping problem

Hello,

I need to structure a document, based on text fragments.

I have a flat xml file like this:

<document>
  <text-fragment function='section' level='1'> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>

  <text-fragment function='section' level='2'> Some text </text-fragment>

  <text-fragment> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>

  <text-fragment function='section' level='2'> Some text </text-fragment>

  <text-fragment> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>

  <text-fragment function='section' level='1'> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>
  <text-fragment> Some text </text-fragment>

<document>

and I want to structure the document like this:

<document>
   <section>
        Some text-fragments ...
        <section>
             Some text-fragments ...
        </section>
   </section>
   <section>
        ... Some fragments for the second section ...
   </section>
</document>

Can you give me some methods, hints, references on how to do this ?
I have already looked on Muenchian grouping, xslt2 groups, but I
cannot find the way to do it.

Thanks for your replies and your time ..;

Vincent De Groote