[whatwg] Undo/Redo events

[Daniel Danilatos]

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