The pipeline
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" name="main" version="3.0">
<p:input port="source">
<doc1/>
</p:input>
<p:input port="secondary">
<doc2/>
</p:input>
<p:output port="result"/>
<p:if test="local-name(collection()[1]/*)='doc2' and local-name(collection()[2]/*)='doc1'" collection="true">
<p:with-input pipe="secondary@main source@main"/>
<p:identity>
<p:with-input>
<right/>
</p:with-input>
</p:identity>
</p:if>
<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">The document root is not “result”.</s:assert>
<s:assert test="result/right">The result is not right.</s:assert>
</s:rule>
</s:pattern>
</s:schema>
