The `User` and `Group` elements are defined in the Util extension namespace, different from the default namespace, and so the prefix is required. Without it, XML validation fails:

<pre>
C:\work\puppet_for_the_win\wix\puppet.wxs(32) : error CNDL0005 : The Product element contains an unexpected child element 'Group'.
C:\work\puppet_for_the_win\wix\puppet.wxs(378) : error CNDL0005 : The Component element contains an unexpected child element 'User'.
</pre>

What's weird though is that RegistrySearch is also from Util extension, but is declared without a prefix....