viewport-022 (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:viewport match="body1">
      <p:with-input>
         <p:inline content-type="application/json" expand-text="false">
                  { "key" : "value" }
               </p:inline>
      </p:with-input>
      <p:add-attribute match="/*" attribute-name="att" attribute-value="3"/>
   </p:viewport>
</p:declare-step>