By default, layout items displayed within the Customization Form are sorted against captions in alphabetical order. To custom sort these layout items, implement a comparer (an object that supports the System.Collections.IComparer interface) and assign it to the HiddenItemsSortComparer property.
The order of fixed items (Empty Space Items, Labels, Separators and Splitters) cannot be changed using the HiddenItemsSortComparer. These items are always sorted in alphabetical order.