public virtual void AddRange(KeyedCollection <T> items)
        {
            if (items == null)
            {
                return;
            }

            AddRange(items.Keys, items.GetItems());
        }
 public virtual ReadOnlyKeyedCollection <T> Clone()
 {
     return(new ReadOnlyKeyedCollection <T>(_coll.Keys, _coll.GetItems()));
 }