The pipeline
<p:declare-step xmlns:ex="http://extension-step.org" xmlns:p="http://www.w3.org/ns/xproc" name="main" version="3.0">
<p:output port="result"/>
<p:declare-step type="ex:test" use-when="p:step-available('ex:test1')">
<p:output port="result"/>
<p:identity>
<p:with-input>
<doc/>
</p:with-input>
</p:identity>
</p:declare-step>
<p:declare-step type="ex:test1" use-when="p:step-available('ex:test2')">
<p:output port="result"/>
<p:identity>
<p:with-input>
<doc/>
</p:with-input>
</p:identity>
</p:declare-step>
<p:declare-step type="ex:test2" use-when="true()">
<p:output port="result"/>
<p:identity>
<p:with-input>
<doc/>
</p:with-input>
</p:identity>
</p:declare-step>
<p:identity>
<p:with-input>
<result>
<test>{p:step-available('ex:test')}</test>
<test1>{p:step-available('ex:test1')}</test1>
<test2>{p:step-available('ex:test2')}</test2>
</result>
</p:with-input>
</p:identity>
</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/test/text()='true'">p:step-available for 'ex:test' is wrong.</s:assert>
<s:assert test="result/test1/text()='true'">p:step-available for 'ex:test1' is wrong.</s:assert>
<s:assert test="result/test2/text()='true'">p:step-available for 'ex:test2' is wrong.</s:assert>
</s:rule>
</s:pattern>
</s:schema>
