You must encode the less than ("<") and greater than (">") characters in the string, as shown in the following code example:

<Properties>
&lt;Columns&gt;
&lt;Column Name="title"/&gt;
&lt;Column Name="link"/&gt;
&lt;Column Name="description"/&gt;
&lt;/Columns&gt;
</Properties>

Optional: No

xmlns: "http://schemas.microsoft.com/Search/2007/location"

Reference

Concepts