BOOL Undo();
Use to undo the last edit-control operation.
An undo operation can also be undone. For example, you can restore deleted text with the first call to Undo, and remove the text again with a second call to Undo as long as there is no intervening edit operation.
For a single-line edit control, the return value is always TRUE. For a multiple-line edit control, the return value is TRUE if the undo operation is successful, or FALSE if the undo operation fails.
CEdit::CanUndo, EM_UNDO