grr your test document had two L2.1 sections which caused me some grief
trying to work out why it numbered the second one 2.2;-)

If I understand what you want, something like this:

$ saxon9 dpbook.xml dpbook.xsl
<?xml version="1.0" encoding="UTF-8"?>
<block role="1" number="1">
   <title role="1">L1</title>
   <block role="2" number="1.1">
      <title role="2">L1.1</title>
      <para>This document defines an XML schema for  ....</para>
   </block>
   <block role="2" number="1.2">
      <title role="2">L1.2</title>
      <para>The normative XML Schema for the OpenDoc ....</para>
   </block>
</block>

I didn't want the nesting (it's to move on to docbook
simplesect elements next, which need to be at para level)
but I think that won't matter.

Thanks.
regards

--
Dave Pawson
XSLT XSL-FO FAQ.
http://www.dpawson.co.uk