Saxon

<?xml version="1.0" encoding="utf-8"?>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"

version="3.0"

xmlns:xs="http://www.w3.org/2001/XMLSchema"

xmlns:mf="http://example.com/mf"

xmlns:ex="http://example.com/ex"

exclude-result-prefixes="#all"

expand-text="yes">

<xsl:function name="mf:group-chunks" as="item()*" streamability="absorbing">

<xsl:param name="items" as="item()*"/>

<xsl:param name="chunk-size" as="xs:integer"/>

<xsl:param name="handle-chunk" as="function(item()*) as item()*"/>

<xsl:for-each-group select="$items" group-adjacent="(position() - 1) idiv $chunk-size">

<xsl:sequence select="$handle-chunk(current-group())"/>

</xsl:for-each-group>

</xsl:function>

<xsl:function name="ex:wrap-rows" as="element()" streamability="absorbing">

<xsl:param name="group" as="element()*"/>

<xsl:param name="wrapper-name" as="xs:QName"/>

<xsl:element name="{$wrapper-name}" namespace="{namespace-uri-from-QName($wrapper-name)}">

<xsl:sequence select="$group"/>

</xsl:element>

</xsl:function>

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

<xsl:mode streamable="yes"/>

<xsl:template match="root">

<xsl:copy>

<xsl:sequence select="mf:group-chunks(item, 3, ex:wrap-rows(?, QName((), 'chunk')))"/>

</xsl:copy>

</xsl:template>

<xsl:template match="/">

<xsl:next-match/>

<xsl:comment xmlns:saxon="http://saxon.sf.net/">Run with {system-property('xsl:product-name')} {system-property('xsl:product-version')} {system-property('Q{http://saxon.sf.net/}platform')}</xsl:comment>

</xsl:template>

</xsl:stylesheet>