On Thu, Apr 5, 2018 at 11:08 PM Masayuki Nakano <masay...@d-toybox.com>

> On 4/6/2018 2:50 AM, Ehsan Akhgari wrote:
> > Hi Masayuki,
> >
> > First of all, thank you for taking on this task.  I have a few questions.
> >
> > * What does the backwards compatibility story for these changes look
> > like?  Would we end up for example throwing exceptions or returning a
> > different value from execCommand/queryCommandState/etc for one of the
> > existing two commands?  If there are any backwards compatibility
> > concerns, what are your plans for them?  Note that these two commands
> > are extremely popular in existing code that knows about Gecko (since it
> > typically has to start off by disabling this UI as you've noted.)
> It *might* be possible that a few web apps (including intranet only
> apps) may allow users to resize some elements, edit table structure
> and/or move absolute positioned elements with these built-in UI only on
> Firefox. If such apps actually exist, they can enable the Gecko specific
> UI explicitly with using execCommand.  Then, we can collect actual usage
> with telemetry.

If such apps don't use execCommand to explicitly enable these commands,
they will be breaking with this change, wouldn't they?  If we are
interested in knowing about whether this is a problem, there's the
possibility of collecting telemetry beforehand too.  For example, we can
collect telemetry upon the usage of these UIs (i.e., when a user interacts
with them) and record information about whether the application has called
one of these commands explicitly to enable the UI beforehand.

If we don't collect this telemetry beforehand, we're effectively assuming
that the breakage of this kind will be low enough that we are considering
its risk low and acceptable.

> > * Why are we *adding* a new command for enabling the absolute
> > positioning UI if we believe this UI is not useful and should be
> > disabled?  Do we have any indication that web developers want to use
> > this UI in some cases, and for Firefox only?  Have we heard any plans
> > from other browser vendors that they're interested to add support for
> > similar UI in the future?  The Github issue you linked to makes that
> > sound unlikely.  Wouldn't it be better to just disable the absolute
> > positioning UI?
> I think that Gecko specific feature may cause unexpected result for web
> apps and could cause unexpected error on some web apps, then, at worst,
> Firefox is banned by UA sniffing.

Hmm, if the risk of removing this UI is so high, then shouldn't we collect
some telemetry data that shows that removing it is safe before attempting
to do so?

(FWIW I don't understand how this UI showing and not showing can break an
editing app so badly that web developers start to ban Firefox UAs.  One way
I can imagine is if they attempt to provide their own similar UI and ours
overrides it, but since we are talking about changing things to hide the UI
that we used to show, I don't think that's the risk you have in mind.)

> Making it's disabled by default but
> making it possible to enable with execCommand, we can collect actual
> usage with telemetry as I said above.

I think we can collect some telemetry data today.  For example, we can
collect data on how many HTML editor instantiations see the absolute
positioning UI, and also how many of the times we display this UI the user
ends up interacting with it.

The problem with adding a new command and try to collect telemetry after
that is that you're expecting Web developers to first update their code to
use the new command before any meaningful telemetry data can be gathered,
and then our hope would be that the data would suggest that the feature is
unused so that we can tell the few Web developers who did update their code
to use the new command to update it again to remove the command once we
decide to remove this UI based on low usage.  :-)

> > * What is our long term plan for this UI, do we want to keep them around
> > or is this us deprecating the UI with the ultimate intention of
> > measuring their usage so that we can eventually remove them?  I think
> > removing this UI is at least desirable from the implementation
> > standpoint.  The way that the native anonymous content this UI uses is
> > hooked up (in
> >
> https://searchfox.org/mozilla-central/rev/f860c2bf00576959b07e2d9619c7b5088b0005be/editor/libeditor/HTMLAnonymousNodeEditor.cpp#143
> )
> > is different than everything else inside Gecko and has historically been
> > a source of bugs, and we've never invested any effort to improve it
> > since we believed the UI wasn't really worth the investment...
> I think that we'll get evidence which indicate nobody uses those Gecko
> specific feature, we can move those UI into comm-central or just remove
> them completely.

Hmm, if we want to keep them around for comm-central, then I'm not all that
certain if moving the code out of m-c is beneficial since this code impacts
the way that NAC frames get contructed (by adding an alternative path to
the "usual" way of doing that in Gecko), so keeping the code in m-c would
mean that we could at least keep testing it and make sure that we don't
break it in horrible ways in the future...  My main point was that it would
be nice to get rid of this alternate code path if we can make nobody depend
on it.
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