pipe-001 (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="producer">
      <p:with-input>
         <doc a="42"/>
      </p:with-input>
   </p:identity>
   <p:sink/>
   <p:add-attribute attribute-name="att">
      <p:with-input>
         <result/>
      </p:with-input>
      <p:with-option name="attribute-value" select="/doc/@a" pipe="@producer1"/>
   </p:add-attribute>
</p:declare-step>