bug#36717: 25.3; greek.el: deprecated vowel+oxia combinations should be replaced with vowel+tonos counterparts

[Robert Alessi <alessi@robertalessi.net>]

Thank you for these valuable items of information, Basil.  I will do
some research and report back no later than tomorrow.

Robert

On Thu, Jul 18, 2019 at 07:16:34PM +0100, Basil L. Contovounesios wrote:
> Robert Alessi <alessi@robertalessi.net> writes:
> 
> > As of 2016, the latest versions of Unicode (as of 2016) have now
> > formally deprecated and removed the vowel+oxia combinations from the
> > Greek extended range, leaving only the vowel+tonos from the basic Greek
> > and Coptic range.
> 
> Where is the deprecation documented?  What do you mean by "removed"?
> AFAIK all of the "deprecated" codepoints are still part of the latest
> Unicode standard[1].
> 
> > As a result of this deprecation, the sixteen characters found in
> > greek.el (Quail package for inputting Greek) that use extended
> > codepoints should be replaced with those that use basic codepoints.
> 
> I'm not opposed to such a simple search+replace[2], but I'm no expert on
> these matters (so please bear with me), and I wonder what effects, if
> any, such a change may have.
> 
> AFAICT all occurrences of the "deprecated" codepoints in greek.el appear
> in classical Greek input methods, not the modern Greek input methods
> greek or greek-postfix.  Would users of the classical input methods ever
> want to explicitly use the oxia, not tonos, variants?
> 
> What confuses me is that, AIUI, the "deprecated" codepoints should
> decompose to their Greek and Coptic counterparts[3].  How does Quail
> interplay with Unicode normalisation?
> 
> [1]: https://www.unicode.org/charts/PDF/U1F00.pdf
> [2]: Indeed, I've seen people trip over this discrepancy, but I forgot
>      to follow up on this: https://emacs.stackexchange.com/a/43927/15748
> [3]: http://www.unicode.org/charts/normalization/
> 
> > All affected characters can be found here: -->
> > https://wiki.digitalclassicist.org/Greek_Unicode_duplicated_vowels#Affected_characters
> >
> > Although most Unicode Greek fonts display both versions identically, in
> > some cases, not using basic codepoints can break advanced features such
> > as alternate forms in Greek script.  To take an example, if some feature
> > is supposed to distinguish between regular and `curly' *beta* (β/ϐ) so
> > as to print the `curly' shape if the *beta* is found in medial position,
> > the substitution will succeed in βάρβαρος, but fail in λάβρος just
> > because of the extended codepoint of ά that is used by `greek.el`.
> 
> How does the use of oxia instead of tonos on the alpha affect the
> substitution of the beta?
> 
> Thanks,
> 
> -- 
> Basil