private void HandleRemovedItem (object sender, ItemEventArgs e)
		{
			if (e.Item != Item)
				return;

			Property = null;
		}
		private void HandleAddedItem (object sender, ItemEventArgs e)
		{
			if (e.Item != Item)
				return;

			var container = Source.Value as IAttachedPropertiesContainer;

			Property = container.GetProperty (Item, PropertyName);
		}