Subclassing Silverlight Controls

While I think everyone understands that fact that you can subclass Silverlight controls in code, I think the concept of subclassing code + xaml is less well understood.First off, why would you want to subclass code + xaml? In most cases, you don’t need to.  This is really more of an edge case scenerio.  I have a control which is a Subclassed treeview.  These treeview needs a number of