The pipeline
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" name="pipeline" version="3.0">
<p:output port="result"/>
<p:input port="source">
<document>
<title>Some Title</title>
<para>Some paragraph.</para>
</document>
</p:input>
<p:choose name="choose">
<p:when test="count(//*) mod 2 = 0">
<p:output port="one" primary="true"/>
<p:output port="two">
<p:inline>
<doc/>
</p:inline>
</p:output>
<p:identity>
<p:with-input port="source">
<p:inline>
<p>There are an even number of elements in the document.</p>
</p:inline>
</p:with-input>
</p:identity>
</p:when>
<p:otherwise>
<p:output port="one" primary="true"/>
<p:output port="two">
<p:inline>
<doc/>
</p:inline>
</p:output>
<p:identity>
<p:with-input port="source">
<p:inline>
<p>There are an odd number of elements in the document.</p>
</p:inline>
</p:with-input>
</p:identity>
</p:otherwise>
</p:choose>
<p:wrap-sequence wrapper="wrapper">
<p:with-input port="source">
<p:pipe step="choose" port="one"/>
<p:pipe step="choose" port="two"/>
</p:with-input>
</p:wrap-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:pattern>
<s:rule context="/">
<s:assert test="/wrapper">Root element is not 'wrapper'.</s:assert>
<s:assert test="/wrapper/p">Root element does not have a child 'p'.</s:assert>
<s:assert test="/wrapper/p/text()='There are an odd number of elements in the document.'">Text of 'p' is not 'There are an odd number of elements in the document.'</s:assert>
<s:assert test="/wrapper/doc">Root element does not have a child 'doc'.</s:assert>
</s:rule>
</s:pattern>
</s:schema>