The pipeline
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" name="pipeline" version="3.0">
<p:input port="source"/>
<p:output port="result"/>
<p:identity name="pr">
<p:with-input>
<p:pipe step="pipeline" port="source"/>
<p:pipe step="pipeline" port="source"/>
<p:pipe step="pipeline" port="source"/>
<p:pipe step="pipeline" port="source"/>
</p:with-input>
</p:identity>
<p:wrap-sequence name="splitseq" wrapper="sequence" group-adjacent="floor(position() div 2)"/>
<p:wrap-sequence wrapper="result"/>
</p:declare-step>
Schematron validation
<s:schema xmlns="http://www.w3.org/1999/xhtml" xmlns:s="http://purl.oclc.org/dsdl/schematron" queryBinding="xslt2">
<s:pattern>
<s:rule context="/">
<s:assert test="result">Root element is not 'result'.</s:assert>
<s:assert test="count(result/child::node())=3">Root element should have three children.</s:assert>
<s:assert test="count(result/sequence)=3">All children of root element should be 'sequence'.</s:assert>
<s:assert test="count(result/sequence[1]/child::node())=1">First sequence element should have one child.</s:assert>
<s:assert test="count(result/sequence[2]/child::node())=2">Second sequence element should have two children.</s:assert>
<s:assert test="count(result/sequence[3]/child::node())=1">Third sequence element should have one child.</s:assert>
<s:assert test="result/sequence[1]/doc">First sequence element should have one 'doc' child.</s:assert>
<s:assert test="count(result/sequence[2]/doc)=2">Second sequence element should have two 'doc' children.</s:assert>
<s:assert test="result/sequence[3]/doc">Third sequence element should have one 'doc' child.</s:assert>
</s:rule>
</s:pattern>
</s:schema>
