title: MVVM-Light PropertyChanged ViewModelBase
body: <p>I would like to understand how the MVVM light toolkit raises the PropertyChanged event.  </p>
  
  <p>I have a feeling that this may be obvious... but I can't satisfy my curiousity without 100% clarity!</p>
  
  <p>I know that this event is raised for each RaisePropertyChanged called, but I'm confused as to why PropertyChanged is raised when the HasValidationErrors property is changed as well?  </p>
  
  <p>Thanks,
  Richard</p>