title: How to catch SourceUpdated for nested children of window?
body: <p>I would like to know when any input element on my Window has its Binding source updated.</p>
  
  <p>The input elements could be TextBox, RadioButton, Slider, ComboBox etc, and may be nested within UserControls or Panels.</p>
  
  <p>Catching SourceUpdated would be nice, but it is not a routed event so is not bubbled to the parent.</p>
  
  <p>Is there a simple way to do this?</p>