depends 029 (AB)

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:identity>
      <p:with-input>
         <doc1/>
         <doc2/>
      </p:with-input>
   </p:identity>
   <p:viewport match="/" depends="wrapper" name="viewport">
      <p:identity/>
   </p:viewport>
   <p:wrap-sequence name="wrapper" depends="viewport">
      <p:with-input>
         <doc/>
      </p:with-input>
      <p:with-option name="wrapper" select="'wrapper'">
         <p:empty/>
      </p:with-option>
   </p:wrap-sequence>
</p:declare-step>