Output port declaration 008 (AB)

The pipeline

<p:declare-step xmlns:err="http://www.w3.org/ns/xproc-error"
                xmlns:p="http://www.w3.org/ns/xproc"
                xmlns:t="http://xproc.org/ns/testsuite/3.0" name="main" version="3.0">
   <p:input port="source">
      <doc/>
   </p:input>
   <p:output port="result">
      <p:pipe port="source"/>
   </p:output>
   <p:identity>
      <p:with-input>
         <doc2/>
      </p:with-input>
   </p:identity>
</p:declare-step>