[whatwg] UndoManager questions

[Ryosuke Niwa]

On Sat, May 26, 2012 at 8:01 PM, Alex Vincent <ajvincent at gmail.com> wrote:

> For those not familiar, the spec lives here:
> http://rniwa.com/editing/undomanager.html


It has been moved to
http://dvcs.w3.org/hg/undomanager/raw-file/tip/undomanager.html


> * The spec is inconsistent in a few places.  For instance, in the green
> non-normative section, clearUndo states:
> Removes entries in the undo transaction
> history<http://rniwa.com/editing/undomanager.html#undo-transaction-history
> >before
> position<
> http://rniwa.com/editing/undomanager.html#dom-undomanager-position>and
> resets
> position<
> http://rniwa.com/editing/undomanager.html#dom-undomanager-position>to
> 0.
>

This statement in the non-formative section is correct.

However, in the normative part, it states:
> The clearUndo() method must remove all entries in the undo transaction
> history <
> http://rniwa.com/editing/undomanager.html#undo-transaction-history>after
> the undo
> position <http://rniwa.com/editing/undomanager.html#undo-position>.
>

This statement is incorrect. Will fix.

* The spec mentions a "DOM transaction
> group<http://rniwa.com/editing/undomanager.html#dom-transaction-group>",
> but does not define that.
>

Will fix.

* When adding a transaction to a DOMTransaction[] as part of execute's
> merge being true, do we add it to the beginning or the end of the
> list? This matters for .item().


I meant at the end, but now that I realize this is inconsistent with the
way entries in the undoManager is ordered. Will change so that it'll be
added at the beginning instead.

* Exception handling is woefully undefined in this spec:
> ** If my transaction throws an exception during UndoManager.execute(), how
> should that be handled? What happens to transaction groups that were
> previously undone?
> ** If my transaction throws an exception during .undo(), how should that be
> handled?
> ** Ditto redo.
>

Let's start a new thread about this.

* What precisely lives at UndoManager.item(0)?  The most recently completed
> transaction, or the oldest?
>

The most recent.

* When UndoManager.execute() is called with an object not implementing
> .undo, or .redo, should we fire some kind of warning to the user?  What
> should happen when we try to undo that transaction?
>

There are valid use cases for creating transactions without undo or redo
method (e.g. need to do something only in undo such as updating toolbar).

- Ryosuke