Pipe attributes 002

The pipeline

<p:declare-step xmlns:err="http://www.w3.org/ns/xproc-error" xmlns:p="http://www.w3.org/ns/xproc" name="main" version="3.0">
   <p:output port="result"/>
   <p:identity name="one">
      <p:with-input port="source">
         <t:doc>One</t:doc>
      </p:with-input>
   </p:identity>
   <p:identity name="two">
      <p:with-input port="source">
         <t:doc>Two</t:doc>
      </p:with-input>
   </p:identity>
   <p:identity name="three">
      <p:with-input port="source">
         <t:doc>Three</t:doc>
      </p:with-input>
   </p:identity>
   <p:identity name="combined">
      <p:with-input port="source" pipe="three two one">
         <p:document href="pipe.xpl"/>
      </p:with-input>
   </p:identity>
   <p:wrap-sequence wrapper="docs"/>
</p:declare-step>