[whatwg] Feedback on UndoManager spec

Ryosuke Niwa rniwa at webkit.org
Thu Oct 27 16:04:35 PDT 2011

On Thu, Oct 27, 2011 at 10:48 AM, Aryeh Gregor <ayg at aryeh.name> wrote:

> On Wed, Oct 26, 2011 at 2:39 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:
> > I meant properties authors added to nodes. e.g.
> > span.myProperty = true;
> > Should span be removed by some automatic transaction, authors may expect
> it
> > to be restored on undo.
> That sounds like the ideal behavior, unless it's too difficult to
> implement.  If authors just used Node.dataset, that would solve their
> problem, but it would be better to behave as expected to start with.

Since Gecko and WebKit can both implement this, I'd expect other UAs to do
the same. I'll update the spec accordingly.

> The assumption is transaction works like a regular object unless otherwise
> > stated. I guess I can cite your example though.
> Some APIs copy objects in some way instead of maintaining a reference.
>  For instance, in WebKit, Selection.getRangeAt() doesn't return the
> same object you added with Selection.addRange() (although the spec
> currently says it should).  It seems best to be explicit.

In the revised spec, I'd say it'll be an entry in the undo transaction
history so the wording there should make clear that they're identical

>> But this doesn't define what happens in the face of manual
> >> transactions.  Also, it's not precise even if there are no manual
> >> transactions.
> >
> > UAs don't do anything for manual transactions. They just call
> > unapply/reapply.
> I mean, if there's a mix of automatic and manual transactions, and the
> manual transactions don't restore the exact same DOM, nothing says how
> the UA should unapply/reapply the automatic transactions.  It just
> says "the user agent still must do its best effort to restore the DOM
> state."

Right. If authors decide to mess with DOM state of the highest node affected
by an automatic transaction, user agents can't do anything to fix that.

 What's the use-case for manual transactions anyway?  I'm sure it's
> been discussed, but your spec doesn't say.  It could use an example.

To be able to mix automatic transactions and manual transactions. Consider
an application that lets you edit both text and drawing on canvas. Such an
app may implement drawing action on canvas as a manual transaction while
adding some extra editing commands as automatic transactions and manage them
all in the same undo manager.

> This is well defined in terms of DOM state. The spec says UAs should
> restore
> > the DOM state
> > so it all depends on how DOM state is defined.
> > I also vaguely remember Ehsan telling me Gecko might have a trouble
> > restoring the exactly same object
> > on undo/redo because of the way its undo and redo are implemented.
> Well, at some point we want to make sure we have interop if possible,
> unless it's really performance-critical that this be UA-dependent.

IMO, it's critical that this part is left implementation dependent.

- Ryosuke

More information about the whatwg mailing list