private IList <Element> GetChildren(object parent, ITypeHandler parentHandler)
        {
            if (!childrenCached)
            {
                var enumerator = parentHandler.GetChildren(parent, displayOptions);
                while (enumerator.MoveNext())
                {
                    childrenCache.Add(enumerator.Current);
                }
                childrenCached = true;
            }

            return(childrenCache);
        }