In reading the spec section 7.10 concerning Undo history, it's not clear to me if it's possible to prevent the browser's default behavior for a user-triggered undo or redo action. In Wave, we need to implement special undo/redo behavior using operational transform, to avoid undoing concurrent operations from other users. More abstractly, we want to control the undo/redo behavior ourselves, but still get the events triggered by the browser from actions like Ctrl+Z, context menu -> Undo, and Edit -> Undo. (Currently we only manually handle the key combo and cancel the key event).
Dan
