Comment on A.2.7 Provide an undo function. [Priority 2]

Do we need the last two success criteria for A.2.7 Provide an undo 
function. [Priority 2] ? I think they may actually be too much for 
Web-based tools running on browsers that only support a single undo. 
Unless we mean the second undo can undo the first (a redo) but I don't 
think that's what we mean. Maybe they would be better as techniques.

- Actions that modify content must be either reversible with an undo 
function or include a warning to the author that the action is 
irreversible.
- The author must be able to perform multiple undos.
- The author must be able to undo any series of undos

Cheers,
Jan