depends 003 (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 name="first">
      <p:with-input>
         <doc1/>
      </p:with-input>
   </p:identity>
   <p:identity>
      <p:with-input>
         <doc2/>
      </p:with-input>
      <p:with-option name="depends" select="'first'"/>
   </p:identity>
</p:declare-step>