Call the Undo method to Undo the last control operation. The Undo method have effect only if the AllowUndoRedo property is True. The CTRL+Z performs the last undo operation, while the CTRL+Y redoes the next action in the control's Redo queue. The Redo redoes the next action in the control's redo queue.  The CanUndo property retrieves a value that indicates whether the control may perform the last Undo operation. The CanRedo property retrieves a value that specifies whether the control can execute the next operation in the control's Redo queue. The URChange(exUndo/exRedo) event notifies your application whenever an Undo/Redo operation is performed. 

The records of the Undo/Redo queue may contain actions in the following format:

• "AddItem;ITEMINDEX", indicates that a new item has been created
• "RemoveItem;ITEMINDEX", indicates that an item has been removed
• "ChangeItemPos;ITEMINDEX", indicates that an item changes its position or / and parent
• "ChangeCellValue;ITEMINDEX;CELLINDEX", indicates that the cell's value has been changed
• "ChangeCellState;ITEMINDEX;CELLINDEX", indicates that the cell's state has been changed

Also, the Undo/Redo queue may include:

• "StartBlock", specifies that a block of operations begins
• "EndBlock", specifies that a block of operations ends

The UndoListAction property lists the Undo actions that can be performed in the control. Use the UndoRemoveAction method to remove the last actions from the undo queue.