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xml - Sectioning different heading levels

The goal is to group elements starting with different heading levels into sections nested according to those levels.

Problem is similar to XSLT: moving a grouping html elements into section levels. The difference here is that heading levels are not in strict order.

To give a simplified example, I want to transform an input like

<body>
    <p>0.1</p>
    <p>0.2</p>

    <h2>h2.1</h2>
    <h3>h3.1</h3>
    <p>3.1</p>
    <p>3.2</p>

    <h1>h1.1</h1>
    <p>1.1</p>
    <h3>h3.2</h3>
    <p>3a.1</p>
    <p>3a.2</p>
</body>

into this desired output:

<document>
   <body>
      <p>0.1</p>
      <p>0.2</p>
      <section level="2">
         <h2>h2.1</h2>
         <section level="3">
            <h3>h3.1</h3>
            <p>3.1</p>
            <p>3.2</p>
         </section>
      </section>
      <section level="1">
         <h1>h1.1</h1>
         <p>1.1</p>
         <section level="3">
            <h3>h3.2</h3>
            <p>3a.1</p>
            <p>3a.2</p>
         </section>
      </section>
   </body>
</document>

This is what I have tried so far, using some modifications to the solution given in XSLT: moving a grouping html elements into section levels:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet 
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:mf="http://example.com/mf"
    exclude-result-prefixes="xs mf"
    version="2.0">

    <xsl:output indent="yes"/>

    <xsl:template match="body">
        <document>
            <xsl:copy>
                <xsl:apply-templates select="@*"/>
                <xsl:sequence select="mf:group(*, 1)"/>
            </xsl:copy>
        </document>
    </xsl:template>

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



    <xsl:function name="mf:group" as="node()*">
        <xsl:param name="elements" as="element()*"/>
        <xsl:param name="level" as="xs:integer"/>

        <xsl:for-each-group select="$elements" 
            group-starting-with="*[
               mf:isHead(local-name()) and 
                 (mf:getHLevel(local-name()) = $level or
                  count(preceding::*[mf:isHead(local-name())]) = 0 
                 )
               ]">
            <xsl:choose>
                <xsl:when test="self::*[mf:getHLevel(local-name()) &lt; 999]">
                    <xsl:variable name="myLevel" 
                                  select="mf:getHLevel(local-name())"/>
                    <section level="{$myLevel}">
                        <xsl:copy>
                           <xsl:apply-templates select="@*, node()"/>
                        </xsl:copy>
                        <xsl:sequence 
                            select="mf:group(current-group() except ., $myLevel + 1)"/>
                    </section>
                </xsl:when>
                <xsl:otherwise>
                    <xsl:apply-templates select="current-group()"/>
                </xsl:otherwise>
            </xsl:choose>
        </xsl:for-each-group>
    </xsl:function>

    <!-- Functions:
         mf:isHead(string):    tests whether string is a headline-name (h1, h2,...)
         mf:getHLevel(string): gets level of heading (h1 -> 1, h2 -> 2, ..., no heading -> 999)
         -->
    <xsl:function name="mf:getHLevel" as="xs:integer">
        <xsl:param name="s"/>
        <xsl:value-of>
          <xsl:choose>
            <xsl:when test="mf:isHead($s)">
                <xsl:value-of select="xs:integer(replace($s,'.*?(d+).*','$1'))"/>                
            </xsl:when>
            <xsl:otherwise>
                <xsl:value-of select="999"/>
            </xsl:otherwise>
          </xsl:choose>
       </xsl:value-of>
    </xsl:function>

    <xsl:function name="mf:isHead" as="xs:boolean">
        <xsl:param name="s"/> 
        <xsl:value-of select="matches($s,'hd+')"/>
    </xsl:function>
</xsl:stylesheet>

I'm pretty sure that the conditions in @group-starting-with are wrong. Namely, count(preceding::*[mf:isHead(local-name())]) = 0 seems to not check, whether a heading-element is the first within the current sequence of elements. But I can't figure out what modifications are needed to achieve the desired output, so any help is appreciated.

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1 Answer

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I would simply let the function group by the current level and stop at the maximum level (which is 6 in HTML):

<xsl:stylesheet
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  version="2.0"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:mf="http://example.org/mf"
  exclude-result-prefixes="xs mf">

<xsl:function name="mf:group" as="node()*">
  <xsl:param name="nodes" as="node()*"/>
  <xsl:param name="level" as="xs:integer"/>
  <xsl:for-each-group select="$nodes" group-starting-with="*[starts-with(local-name(), concat('h', $level))]">
    <xsl:choose>
      <xsl:when test="self::*[starts-with(local-name(), concat('h', $level))]">
        <section level="{$level}">
          <xsl:apply-templates select="."/>
          <xsl:sequence select="mf:group(current-group() except ., $level + 1)"/>
        </section>
      </xsl:when>
      <xsl:when test="$level lt 6">
        <xsl:sequence select="mf:group(current-group(), $level + 1)"/>
      </xsl:when>
      <xsl:otherwise>
        <xsl:apply-templates select="current-group()"/>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:for-each-group>
</xsl:function>

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

<xsl:template match="body">
  <xsl:copy>
    <xsl:sequence select="mf:group(node(), 1)"/>
  </xsl:copy>
</xsl:template>

</xsl:stylesheet>

Obviously the level to search for could be provided as a parameter instead of hardcoding it in the stylesheet:

<xsl:stylesheet
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  version="2.0"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:mf="http://example.org/mf"
  exclude-result-prefixes="xs mf">

<xsl:param name="max-level" as="xs:integer" select="6"/>

<xsl:param name="name-prefix" as="xs:string" select="'h'"/>

<xsl:output method="html" indent="yes"/>

<xsl:function name="mf:group" as="node()*">
  <xsl:param name="nodes" as="node()*"/>
  <xsl:param name="level" as="xs:integer"/>
  <xsl:for-each-group select="$nodes" group-starting-with="*[starts-with(local-name(), concat($name-prefix, $level))]">
    <xsl:choose>
      <xsl:when test="self::*[starts-with(local-name(), concat($name-prefix, $level))]">
        <section level="{$level}">
          <xsl:apply-templates select="."/>
          <xsl:sequence select="mf:group(current-group() except ., $level + 1)"/>
        </section>
      </xsl:when>
      <xsl:when test="$level lt $max-level">
        <xsl:sequence select="mf:group(current-group(), $level + 1)"/>
      </xsl:when>
      <xsl:otherwise>
        <xsl:apply-templates select="current-group()"/>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:for-each-group>
</xsl:function>

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

<xsl:template match="body">
  <xsl:copy>
    <xsl:sequence select="mf:group(*, 1)"/>
  </xsl:copy>
</xsl:template>

</xsl:stylesheet>

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