p:set-attributes-001 (NW)

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:set-attributes match="/doc" attributes="map { 'xmlns': '5' }">
      <p:with-input>
         <doc attribute="3">
                  Some text
                  <!-- a comment -->
                  <?pi?>
               </doc>
      </p:with-input>
   </p:set-attributes>
</p:declare-step>