p:choose-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>
      <p:with-input>
         <doc/>
      </p:with-input>
   </p:identity>
   <p:choose>
      <p:when test="/doc">
         <p:output port="default"/>
         <p:identity/>
      </p:when>
      <p:otherwise>
         <p:identity/>
      </p:otherwise>
   </p:choose>
</p:declare-step>