internal void CollapseAll()
        {
            for (int i = Count - 1; i > 0; i--)
            {
                TextElement oldItem = this[i] as TextElement;

                if (oldItem == null)
                {
                    continue;
                }

                TextElement newItem = oldItem.Collapse();

                if (newItem == null)
                {
                    RemoveAt(i);
                }
                else
                {
                    SetItem(i, newItem);
                }
            }
        }