XS 001 -24 (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 depends="adder">
      <p:with-input>
         <result/>
      </p:with-input>
   </p:identity>
   <p:add-attribute name="adder" match="/*" attribute-name="att" attribute-value="42">
      <p:with-input>
         <doc>{.}</doc>
      </p:with-input>
   </p:add-attribute>
</p:declare-step>