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[whatwg] UndoManager: restoring selection after undoing deletion

From: Ryosuke Niwa <rniwa@webkit.org>
Date: Thu, 20 Oct 2011 00:16:44 -0700
Message-ID: <CABNRm60BdCw4ZyKNO0a=m7pQEV-YJFF3TJmNHWh_gCTr1XRbYg@mail.gmail.com>
Hi,

The way selection is restored on WebKit after undoing selection is different
from the way it is done on Firefox and Internet Explorer.

Say you had "hello world" and "world" is deleted by an user. When the user
undoes the deletion, WebKit selects "world" whereas Firefox and Internet
Explorer do not select "world". WebKit's behavior matches Mac's NSTextView
and we probably would like to keep the current behavior.

However, there's no easy way for the user agent to figure out whether a
given transaction wants to select some contents on undo or not. In fact, we
don't even know whether we want to restore selection at all. If an automatic
transaction was modifying non-text nodes (e.g. SVG line elements), then
restoring selection isn't desirable at all.

I can think of two approaches to solve this problem:

   1. Let automatic transactions also have unapply/reapply and call them
   after user agents had done its work, and make the user agent do nothing in
   regards to selection. We can name them afterUnapply/afterReapply if we want.
   The benefit of this approach is that it's very general and authors can do
   other things as well while the disadvantage being author needs to be fully
   aware of platform-convention of how selection is restore upon undo/redo.

   2. Add a boolean restoreSelection and isDeletion properties to the
   Transaction interface. The user agent restores the selection when the value
   is true and does not restore selection when the value is false. isDeletion
   is true when the transaction is meant to delete contents and false
   otherwise. (Maybe negate the property so that common case will be easy?) The
   user agents can probably use some heuristics to determine whether a given
   transaction is deleting contents or not.

But I don't like either solution so I'm open to your ideas and thoughts on
this.

Best,
Ryosuke Niwa
Software Engineer
Google Inc.
Received on Thursday, 20 October 2011 00:16:44 UTC

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