protected override void Removed(RemoveContentContext context, TPart instance)
 {
     if (OnRemoved != null)
     {
         OnRemoved(context, instance);
     }
 }
 void IContentHandler.Removed(RemoveContentContext context)
 {
     foreach (var filter in Filters.OfType <IContentStorageFilter>())
     {
         filter.Removed(context);
     }
     Removed(context);
 }
 protected virtual void Removed(RemoveContentContext context)
 {
 }