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