Feedback requested for UndoManager and DOM Transaction

Greetings all,

As you maybe all aware, I've been working with developers of
CKEditor, TinyMCE, and Google Docs along with developers from WebKit,
Mozilla, and Opera on new UndoManager and DOM Transaction
specification<http://rniwa.com/editing/undomanager.html> for
the last several months. And it's about time I ask for feedback from
broader audience!

Why? Because *undo and redo are broken on the Web today*. Whenever Web
apps try to add a custom editing operation without using execCommand or do
a "fix up" after browser executes a user editing action, user agents get
confused by DOM mutations made by the apps and won't be able to undo or
redo user editing actions and execCommand. This forces Web apps to
re-implement undo and redo themselves, and in fact, *many rich text editors
store innerHTML of*
*a contenteditable element* as a string in their internal undo
transaction history (a.k.a undo stack).

There is also no way for Web apps to add new undo items and populate undo
and redo menus on user agent's native UI.  In addition, if an editor app
has a widget with input/textarea, then the undo stack of the editor gets
confused when the widget goes away because the undo transaction history
exists only per document.

In order to solve above and numerous other problems, we've come to
a conclusion that we need to *add UndoManager and DOM Transaction*.

*UndoManager* is an interface for managing *undo transaction history*.
 It exists on a document and an element with the undoscope content
attribute.
The main purpose of UndoManager is to communicate the list of undoable
items with the user agent so that the user agent can provide a native UI
(e.g. populating menu items with them).

A *DOM transaction* is a sequence of DOM mutations that can be
applied, unapplied, or reapplied.  There are two types of DOM transactions:

   - *Automatic DOM transaction* - Only the logic to make the initial DOM
   changes is supplied by the author, and the user agent takes care of undo an
   redo. It is *compatible with user editing actions and editing commands*,
   and allows Web apps to easily do custom editing operations or fix up DOM
   after user editing actions.
   - *Manual DOM transaction* - Web apps specify logics to apply, unapply,
   and reapply the transaction and *takes the full control of undo and redo*.
    This transaction is useful for apps such as collaborative editor or canvas
   drawing apps that need to implement custom logic for undo and redo.

You can see more concrete definitions of UndoManager and Transaction at:
https://rniwa.com/editing/undomanager.html and see a list of uses cases at
http://wiki.whatwg.org/wiki/UndoManager_Problem_Descriptions.  I consider
the current proposal to be ready for implementation feedback, and as such,
I plan to prototype it in WebKit and give my own feedback as well.

I sincerely request for your feedback on the proposal, and I will answer
any question(s) you may have about the proposal.

Best regards,
Ryosuke Niwa
Software Engineer
Google Inc.