XSLT: moving a grouping html elements into section levels

Here is an XSLT 2.0 stylesheet:

<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: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="*[local-name() eq concat('h', $level)]">
      <xsl:choose>
        <xsl:when test="self::*[local-name() eq concat('h', $level)]">
          <section level="{$level}">
            <xsl:element name="header{$level}"><xsl:apply-templates/></xsl:element>
            <xsl:sequence select="mf:group(current-group() except ., $level + 1)"/>
          </section>
        </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="/html">
    <document>
      <xsl:apply-templates select="body"/>
    </document>
  </xsl:template>

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

</xsl:stylesheet>

It should do what you asked for, although it does not stop at four nested levels but rather groups as long as it finds h[n] elements.

An XSLT 1.0 solution (essentially borrowed by Jenni Tennison):

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>

 <xsl:template match="html">
   <document><xsl:apply-templates/></document>
 </xsl:template>

 <xsl:template match="body">
   <xsl:apply-templates select="h1" />
 </xsl:template>

 <xsl:key name="next-headings" match="h6"
          use="generate-id(preceding-sibling::*[self::h1 or self::h2 or
                                               self::h3 or self::h4 or
                                               self::h5][1])" />
 <xsl:key name="next-headings" match="h5"
          use="generate-id(preceding-sibling::*[self::h1 or self::h2 or
                                               self::h3 or self::h4][1])" />
 <xsl:key name="next-headings" match="h4"
          use="generate-id(preceding-sibling::*[self::h1 or self::h2 or
                                               self::h3][1])" />
 <xsl:key name="next-headings" match="h3"
          use="generate-id(preceding-sibling::*[self::h1 or self::h2][1])" />
 <xsl:key name="next-headings" match="h2"
          use="generate-id(preceding-sibling::h1[1])" />

 <xsl:key name="immediate-nodes"
          match="node()[not(self::h1 | self::h2 | self::h3 | self::h4 |
                           self::h5 | self::h6)]"
          use="generate-id(preceding-sibling::*[self::h1 or self::h2 or
                                               self::h3 or self::h4 or
                                               self::h5 or self::h6][1])" />

 <xsl:template match="h1 | h2 | h3 | h4 | h5 | h6">
   <xsl:variable name="vLevel" select="substring-after(name(), 'h')" />
   <section level="{$vLevel}">
      <xsl:element name="header{$vLevel}">
        <xsl:apply-templates />
      </xsl:element>
      <xsl:apply-templates select="key('immediate-nodes', generate-id())" />
      <xsl:apply-templates select="key('next-headings', generate-id())" />
   </section>
 </xsl:template>

 <xsl:template match="/*/*/node()" priority="-20">
   <xsl:copy-of select="." />
 </xsl:template>
</xsl:stylesheet>

when this transformation is applied on the following XML document:

<html>
    <body>
        <h1>1</h1>
        <p>1</p>
        <h2>1.1</h2>
        <p>2</p>
        <h3>1.1.1</h3>
        <p>3</p>
        <h2>1.2</h2>
        <p>4</p>
        <h1>2</h1>
        <p>5</p>
        <h2>2.1</h2>
        <p>6</p>
    </body>
</html>

the wanted result is produced:

<document>
   <section level="1">
      <header1>1</header1>
      <p>1</p>
      <section level="2">
         <header2>1.1</header2>
         <p>2</p>
         <section level="3">
            <header3>1.1.1</header3>
            <p>3</p>
         </section>
      </section>
      <section level="2">
         <header2>1.2</header2>
         <p>4</p>
      </section>
   </section>
   <section level="1">
      <header1>2</header1>
      <p>5</p>
      <section level="2">
         <header2>2.1</header2>
         <p>6</p>
      </section>
   </section>
</document>

A more general grouping in XSLT 1.0

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:key name="kHeaderByPreceding"
             match="body/*[starts-with(name(),'h')]"
             use="generate-id(preceding-sibling::*
                                 [starts-with(name(),'h')]
                                 [substring(name(current()),2)
                                   > substring(name(),2)][1])"/>
    <xsl:key name="kElementByPreceding"
             match="body/*[not(starts-with(name(),'h'))]"
             use="generate-id(preceding-sibling::*
                                 [starts-with(name(),'h')][1])"/>
    <xsl:template match="node()|@*" mode="copy">
        <xsl:copy>
            <xsl:apply-templates select="node()|@*" mode="copy"/>
        </xsl:copy>
    </xsl:template>
    <xsl:template match="body">
        <document>
            <xsl:apply-templates select="key('kHeaderByPreceding','')"/>
        </document>
    </xsl:template>
    <xsl:template match="body/*[starts-with(name(),'h')]">
        <section level="{substring(name(),2)}">
            <xsl:element name="header{substring(name(),2)}">
                <xsl:apply-templates mode="copy"/>
            </xsl:element>
            <xsl:apply-templates select="key('kElementByPreceding',
                                             generate-id())"
                                 mode="copy"/>
            <xsl:apply-templates select="key('kHeaderByPreceding',
                                             generate-id())"/>
        </section>
    </xsl:template>
    <xsl:template match="text()"/>
</xsl:stylesheet>

Output:

<document>
    <section level="1">
        <header1>HEADER 1 CONTENT</header1>
        <p>Level 1 para</p>
        <p>Level 1 para</p>
        <p>Level 1 para</p>
        <p>Level 1 para</p>
        <section level="2">
            <header2>Header 2 CONTENT</header2>
            <p>Level 2 para</p>
            <p>Level 2 para</p>
            <p>Level 2 para</p>
            <p>Level 2 para</p>
        </section>
    </section>
</document>

And with a more complex input sample like:

<body>
    <h1>1</h1>
    <p>1</p>
    <h2>1.1</h2>
    <p>2</p>
    <h3>1.1.1</h3>
    <p>3</p>
    <h2>1.2</h2>
    <p>4</p>
    <h1>2</h1>
    <p>5</p>
    <h2>2.1</h2>
    <p>6</p>
</body>

Output:

<document>
    <section level="1">
        <header1>1</header1>
        <p>1</p>
        <section level="2">
            <header2>1.1</header2>
            <p>2</p>
            <section level="3">
                <header3>1.1.1</header3>
                <p>3</p>
            </section>
        </section>
        <section level="2">
            <header2>1.2</header2>
            <p>4</p>
        </section>
    </section>
    <section level="1">
        <header1>2</header1>
        <p>5</p>
        <section level="2">
            <header2>2.1</header2>
            <p>6</p>
        </section>
    </section>
</document>

XSLT: moving a grouping html elements into section levels

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