This feed does not validate.
In addition, interoperability with the widest range of feed readers could be improved by implementing the following recommendations.
<!--
Description: example from http://msdn.microsoft.com/XML/rss/sle/default.aspx
Expect: Error
-->
<rss version="2.0"
xmlns:cf="http://www.microsoft.com/schemas/rss/core/2005"
xmlns:book="http://www.example.com/book">
<channel>
<cf:treatAs>list</cf:treatAs>
<title>Books in My Collection</title>
<link>http://www.example.com/collectionofbooks.htm</link>
<cf:listinfo>
<cf:sort label="Relevance" default="true" />
<cf:sort ns="http://www.example.com/book"
element="firstedition" label="First Edition" data-type="date" />
<cf:group ns="http://www.example.com/book" element="genre" label="Genre" />
</cf:listinfo>
<item>
<title>Great Journeys of the Past</title>
<author>Bob</author>
<description>A wonderful history of great journeys</description>
<book:firstedition>Sat, 07 Sep 2002 00:00:01 GMT</book:firstedition>
<book:genre>Travel</book:genre>
</item>
<item>
<title>Horror Stories, vol 16</title>
<author>Steve</author>
<description>Our favorite horror author provides us with another great collection</description>
<book:firstedition>Thu, 25 Aug 2005 00:00:01 GMT</book:firstedition>
<book:genre>Horror</book:genre>
</item>
</channel>
</rss>