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="identity">
<p:with-input port="source">
<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="p:pipe-sequence"/>
</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:ns uri="http://www.w3.org/ns/xproc" prefix="p"/>
<s:pattern>
<s:rule context="/">
<s:assert test="p:pipe-sequence">Root element is not 'p:pipe-sequence'.</s:assert>
<s:assert test="count(p:pipe-sequence/*)=4">Root element should have 4 children.</s:assert>
<s:assert test="count(p:pipe-sequence/doc)=4">Root element should have 4 children named 'doc'.</s:assert>
</s:rule>
</s:pattern>
</s:schema>
