title: Is there a predefined event to mark that an object has been invalidated?
body: <p>I have an object which has properties. These are wired up with INotifyPropertyChanged. I also have collection properties which implement INotifyCollectionChanged. However, there is no event fired if an item already in a collection is altered.</p>
  
  <p>I would like an event I can use to signal that there has somewhere been a change inside the object - is there one existing already? (it's fairly easy to do by hand, but more consitent if something already exists).</p>