private IEnumerable <object> RootElements(Repository repo)
        {
            List <object> result = new List <object>();

            foreach (object each in repo.GetElements())
            {
                MetaDescription     meta = repo.DescriptionOf(each);
                PropertyDescription containerProperty = meta.ContainerPropertyOrNull();
                if (containerProperty != null)
                {
                    Object container = containerProperty.Read(each);
                    if (container == null)
                    {
                        result.Add(each);
                    }
                }
                else
                {
                    result.Add(each);
                }
            }
            ;
            return(result);
        }