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

[Ehsan Akhgari]

This is a very nice proposal; thanks for working on this, Ryosuke!  I 
have a number of questions and concerns on it, and I would appreciate if 
you can comment on these:

1. The definition of @undoscope seems to not address the question of 
whether the document element should be an Undo Scope or not.

2. @undoscope seems to make it very hard to support the usecase of 
moving the undo scope from an element to another.  (I'm not sure if that 
is a concern that we need to address at all, though).

3. In regard to "Should apply return a boolean value indicating whether 
it successfully applied or not?", answering yes means that we should 
make sure that we're going to be able to cleanly revert a transaction 
when it fails, right?  Also, saying yes here means that we should decide 
what happens if that transaction is in a transaction group.  ... all of 
which makes me want to say no.  :-)

4. In regard to "Need to restore selection as well", is that something 
which we want all the time?  Imagine an "indent" transaction which 
indents a paragraph by increasing its start margin, should it change the 
selection when it's undone?

5. I have serious doubts about the current specification of manual 
transactions.  I don't know why we need to exclude them from group 
transactions, but honestly, I'm not sure why we need to have them at 
all.  What use cases are we trying to address by manual transactions 
that would otherwise be impossible to address with managed transactions?

6. I think if we want to address selection saving/restoring, that part 
belongs to the "Mutation of DOM" section.  We might also need to address 
some other editing related stuff in the DOM state, such as the keyboard 
layout language, selection, etc.

7. I'm not sure if we should leave the interaction of @contenteditable 
and @undoscope unaddressed.  At the very least, we need to specify 
whether by default all contenteditable elements on a web page share the 
same undo manager or not.  If I were to pick the default, I would 
suggest that by default they should all share the document's undo manager.

8. As a last comment, I think a better name for UndoManager is 
TransactionManager, since, well, that's what it really is!  :-)

Cheers,
Ehsan