RE: On language-dependent defaults for character-folding

[Drew Adams <drew.adams@oracle.com>]

> > From what I've seen, this is a complex feature with many corner
> > cases, some of which may not have been encountered yet because it
> > hasn't been "out in the field" except for a few pretests.
> 
> I don't see any corner use cases, just some parts that, for best
> results, should be handled depending on the language of the text.
> What we have now is IMNSHO good enough, although improvements are
> welcome (and need infrastructure we don't currently have).  This is
> a clear case of perfect being the enemy of good.

I don't see anyone arguing that this feature is not "good enough" for
Emacs 25.1.  No one has suggested pulling the feature from the release.

The question is only whether it should be turned on by default.
Posing that question, and even deciding that it is not, is not at
all "a clear case of perfect being the enemy of good."

> > The question is whether it should become the default for all
> > users from the start.

What John said.

> > We can always enable it as a default later, so I
> > don't see a need to hurry. This could be a great feature to
> > introduce as a default in 26.1, if it receives good reception from
> > early adopters in 25.x.
> 
> Why does it have to be a binary all or nothing decision?  Users of a
> few languages found some of the folding patterns incorrect for their
> language -- why not turn only those patterns off in the locales that
> use only those languages?  Why should we have this decision affect
> users who have nothing to do with those few languages?

That's a reasonable question: whether Emacs should have different
default values for this feature for different users/locales.

I tend to think that deciding to do that now would also be a bit
premature, but the question is reasonable.

> Turning this summarily off will also disable features that AFAIR no
> one objected to -- the ability to find á (a 2-character sequence)
> when looking for á (one character), or vice versa.  I fail to see
> how a failure to match by default in this use case would make any
> sense at all.

That "ability to find" would not disappear if char-folding were
off by default.  It is you who sounds like you are now making the
question into all-or-nothing.

> We should make our decisions in this matter based on understanding
> the issues involved, and try very hard not to throw away the baby
> with the bathwater.

I don't see anyone proposing to throw out the bathwater, much less
the baby with it.

Eli, you say here, quite often, that you think discussions about
what the default behavior of a feature should be are typically
fruitless, if not sterile.  But it seems clear that you care quite
a lot about this default behavior.

I'd say let it go.  There will be Emacs 25.2 and beyond.  And users
will try this new feature and give their feedback, which I expect
will be overwhelmingly positive - and informative for further
discussions here.

Based on user feedback and further discussion and analysis here
(this is not going away), Emacs Dev will improve and elaborate this
feature.  We will have better ideas about how to handle all of the
things that are currently not so clear.  There is plenty of time
to decide again whether this or that should be turned on by default.

What seems clear to me for Emacs 25.1 is that the feature should be
included AND that it should be simple to both (1) customize the
default behavior for a given user (i.e., what behavior search starts
with, a la `case-fold-search') and (2) toggle the behavior on the
fly, during Isearch.

Given (1) and (2), users can do what they like, and we can learn
later from them what behaviors might best be adopted for defaulting.