title: Extending the property window in Visual Studio
body: <p>XNA Game Studio somehow extended the properties window in Visual Studio with two new combo boxes, "Importer" and "Processor". These combo boxes contained the available importers and processors defined in code in the current solution, and when these fields were changed, the setting was saved to the corresponding item's metadata in the project file.</p>
  
  <p>I'm curious about how they achieved this? Any information would be appreciated.</p>
  
  <p><img src="https://i.stack.imgur.com/Ei33m.jpg" alt="enter image description here"></p>