Cutting a long story short, I have some files in a rather flat XML
structure which I now want to upgrade to a more sophisticated schema.
The files can have the following structures:

Example 1:
<xml>
  <p>blablabla</p>
</xml>

Example 2:
<xml>
  <p>Aaaaaa</p>
  <break/>
  <p>Bbbbbb</p>
</xml>

Example 3:
<xml>
  <title>Title 1</title>
    <p>Aaaaaa</p>
    <break/>
    <p>Bbbbbb</p>
  <title>Title 2</title>
    <p>Cccccc</p>
</xml>

The point being that the files can have various combinations of titles
and breaks, or none at all. I'm hoping I can get a one-pass solution to
achieve the following results:

Result 1:
<xml>
  <section>
  <p>blablabla</p>
  </section>
</xml>

Result 2:
<xml>
  <section>
    <p>Aaaaaa</p>
  </section>
  <section>
    <p>Bbbbbb</p>
  </section>
</xml>

Result 3:
<xml>
  <chapter id="1">
    <title>Title 1</title>
    <section>
       <p>Aaaaaa</p>
    </section>
    <section>
       <p>Bbbbbb</p>
    </section>
  </chapter>
  <chapter id="2">
   <title>Title 2</title>
   <section>
    <p>Cccccc</p>
   </section>
  </chapter>
</xml>

I have already managed to handle the chapters using the following XSL,
adapted from a sample at http://www.dpawson.co.uk/xsl/sect2/N4486.html:

Chapters.xsl:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="xml">
    <xsl:copy>
      <xsl:apply-templates select="title" mode="walker"/>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="title" mode="walker">
    <xsl:variable name="num"><xsl:value-of
select="position()"/></xsl:variable>
    <chapter id="chap.{$num}">
      <title>
      <xsl:value-of select="."/>
      </title>
      <xsl:apply-templates select="following-sibling::*[1]"
mode="walker"/>
    </chapter>
  </xsl:template>

  <xsl:template match="*" mode="walker">
    <xsl:apply-templates select="."/>
    <xsl:if test="not(following-sibling::*[1]/self::chapter)">
      <xsl:apply-templates select="following-sibling::*[1]"
mode="walker"/>
    </xsl:if>
  </xsl:template>

  <xsl:template match="@* | node()">
    <xsl:copy>
      <xsl:apply-templates select="@* | node()"/>
    </xsl:copy>
  </xsl:template>
</xsl:stylesheet>

I also managed to write some XSL that placed text between breaks into
sections, but combining both seems a bit more tricky. So I thought "I
know, I'll ask some experts". :)