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Subject: Re: [SG16-Unicode] UCD and Private Use Area
From: Corentin Jabot (corentinjabot_at_[hidden])
Date: 2019-08-30 01:21:34


On Fri, Aug 30, 2019, 12:45 AM JeanHeyd Meneide <phdofthehouse_at_[hidden]>
wrote:

> Well, the directives of the SG16 Direction Paper says to avoid excessive
> inventiveness....
>

I would be wary to any inventiveness in terms of departing from the Unicode
spec , let's follow the recommendation of the Unicode consortium, they know
better.

>
> Because the unicode character database properties have pervasive uses in
> Unicode (staring with Normalization, and branching out from there), it
> would be incredibly hard to properly provide all of the C++ algorithms a
> chance to override the database used. You'd have to make sure every single
> algorithm can receive the database; or, define a "weak symbol" from the
> implementation which you then plug with your information. I don't know if
> the Timezone Database (tzdb) in chrono/date can help shed some light on how
> this might be done in a Modern C++ API without breaking implementer backs;
> looking there might be a good start.
>

Timezones are different in that they change a lot, but then again it is not
something users should be able to control and they can't. As I write this
mail it is 8am my time. And as much as I would like to, I don't get to
change that.

> I'm still unsure if it's necessary but if it's going to be customizable
> we'd better make sure it's done right...
>

I argue it isn't desirable.
Wether 'a' is a letter is not a user decision.
Whether a private use character has some properties can be resolved with a
user provided database and algorithms.
Note that tautologically, these properties would not be Unicode properties.

You can understand this message because we share a common understanding of
what each group of black pixel means. PUA has it's uses but it doesn't call
for standard tools because by definition it is not standard. If you start
to have properties on user provided characters, then suddenly none of the
algorithm follow the spec.

Best Wishes,
> JeanHeyd
>



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