<p>Anyone know if there is already a validator for "type" strings?</p>

<p>I want to make sure that the type attributes in my custom config are one of the following:</p>

<pre>
type="TopNamespace.SubNameSpace.ContainingClass, MyAssembly"
type="TopNamespace.SubNameSpace.ContainingClass, MyAssembly, Version=1.3.0.0, Culture=neutral, PublicKeyToken=b17a5c561934e089"
</pre>

<p>Writing one is easy enough, I just don't want to reinvent the wheel.</p>

You'll get an error with resharper's Global Error Analysis if it can't find the namespace or class, but that's not always helpful if your referencing a plugin.
probably the simpliest thing is to put your code to load the app domain in a try catch block.
if the dll is in the bin it will be loaded on startup but it won't throw an error until you use it so if you just new up an instance of ContainingClass. You could pull the namespaces from the config and then try and use each class.