The Undo / Redo Control simply lists the actions that can be undone, allows you to select a certain point to go back to and to clear the list of actions.
1. Undo List
Selecting an entry in the list will undo all listed actions following that entry. If then another entry is selected the entries in between will be undone/redone as necessary.
2. Selected Undo Entry
3. Clear Undo List
Clears the Undo List to avoid actions performed hours ago to clutter the list.