The pipeline
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" version="3.0">
<p:output port="result" sequence="true"/>
<p:for-each name="loop">
<p:with-input>
<p:empty/>
</p:with-input>
<p:output port="out" sequence="true" primary="false">
<p:pipe step="identity" port="result"/>
</p:output>
<p:identity name="identity"/>
</p:for-each>
<p:count>
<p:with-input port="source">
<p:pipe step="loop" port="out"/>
</p:with-input>
</p:count>
</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 prefix="c" uri="http://www.w3.org/ns/xproc-step"/>
<s:pattern>
<s:rule context="/*">
<s:assert test="self::c:result">The pipeline root is not c:result.</s:assert>
<s:assert test="string(.) = '0'">The result isn't "0"</s:assert>
</s:rule>
</s:pattern>
</s:schema>
