Flattening parts of a document heirarchy

I know there are faq's on flattening but as  newbie i'm  a little unclear on 
this.

My problem:

incoming document is something like this:

<doc>
    text text text
    <sec id="sec1">
       <p>text1text1text1</p>
        <sec id="sec1.1">
           <p>text2 text2 text2</p>
        </sec>
       <p>text3 text3 text3</p>
   </sec>
</doc>

i.e <sec> tags are nested to arbitary level.

I need

<doc>
   text text text
   <section id="s1" level="1">
       <p>text1 text1 text1</p>
   </section>
   <section id="s2" level="2">
        <p>text text text</p>
   </section>
   <section id="s3" level="1">
       <p>text3 text3 text3</p>
   </section>
</doc>
 

 thanks in advance,

 Dave.

  
-- 
Dr. David Holden. (Systems Developer)
Crystallography Journals Online: <http://journals.iucr.org>

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