[whatwg] Fixing undo on the Web - UndoManager and Transaction

[Ryosuke Niwa]

Hi all,

I've uploaded my proposal: http://rniwa.com/editing/undomanager.html

Summary of changes:

   - *Section 3.2 Automatic transactions* is rewritten
      - Removed *A proper sequence of automatic transactions*
      - Added *3.2.1. Undoability and Redoability of Automatic
Transactions*to clarify when an automatic transaction can be unapplied
and reapplied
      safely
   - isReapply argument is added to apply method of Transaction interface
   - isAutomatic attribute is added to Transaction interface
   - Partial interfaces are added for Document and Element interfaces to
   define undoManager and undoScope IDL attributes
   - label attribute of Transaction interface can return null now, and the
   spec allows UAs to use a part of the value as supposed to the whole (e.g.
   when it's too long)

- Ryosuke