Hi,
If You modify catalog.xml to two-cascade xml, sript works.
But sorting fields in cascade is probably not correct.
<catalog>
<book>
<author>Dorothy Hoskins</author>
<title>XML and InDesign</title>
<genre>Computer</genre>
<ISBN>144934416X</ISBN>
<website>WEBLINK1</website>
</book>
<book>
<author>Tad Williams</author>
<title>The War of the Flowers</title>
<genre>Fantasy</genre>
<ISBN>0756401356</ISBN>
<website>WEBLINK2</website>
</book>
</catalog>