The pipeline
<p:declare-step xmlns:err="http://www.w3.org/ns/xproc-error" xmlns:p="http://www.w3.org/ns/xproc" version="3.0">
<p:output port="result"/>
<p:option name="var" select="5" as="foo"/>
<p:identity>
<p:with-input port="source">
<doc>{$var}</doc>
</p:with-input>
</p:identity>
</p:declare-step>
