viewport-011 (AB)

The pipeline

<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" version="3.0">
   <p:input port="source"/>
   <p:output port="result"/>
   <p:viewport match="sub">
      <p:variable name="p1" select="p:iteration-position()"/>
      <p:variable name="s1" select="p:iteration-size()"/>
      <!-- a p:group wrapper to tests that p:iteration-position
             and p:iteration-size are not affected -->
      <p:group>
         <p:variable name="p2" select="p:iteration-position()"/>
         <p:variable name="s2" select="p:iteration-size()"/>
         <p:viewport match="para">
            <p:variable name="p3" select="p:iteration-position()"/>
            <p:variable name="s3" select="p:iteration-size()"/>
            <p:add-attribute match="item" attribute-name="pos">
               <p:with-input port="source">
                  <p:inline>
                     <item/>
                  </p:inline>
               </p:with-input>
               <p:with-option name="attribute-value" select="concat($p1, ',', $s1, '-', $p2, ',', $s2, '-', $p3, ',', $s3)"/>
            </p:add-attribute>
         </p:viewport>
      </p:group>
   </p:viewport>
</p:declare-step>