In reference to this discussion:
I solved almost all the problems, but one thing still remains obscure to me.
The difficulty is twofold, since it involves on the one hand creating the correct lookups for the font, on the other hand making sure that the text code applies them in turn correctly.
Now, (Lua)LaTeX with Fontspec and Babel allows you to choose among several options: 1) monotonic modern Greek, 2) polytonic modern Greek, 3) ancient greek (polytonic). In this case the code I use is the following:
<div>\usepackage[italian]{babel}
</div><div>\babelprovide[import]{ancientgreek}</div><div>
\babelprovide[import]{polytonicgreek}</div><div>
\babelprovide[import]{greek}</div><div></div>
I can't find specific tags related to ancient Greek.
I tried using the GRC and GRK specifications (in addition to PGR), which however do not seem to be correct otf tags.
In fact, a verification of the font tells me:
<div>otfinfo -s SimonciniGaramondPro.otf</div><div>
DFLT Default</div><div>
grek Greek</div><div>
grek.GRC Greek / <unknown language> <=======</div><div>
grek.GRK Greek / <unknown language> <=======</div><div>
grek.PGR Greek / Polytonic Greek</div><div>
latn Latin</div><div>
latn.AZE Latin / Azeri</div><div>
latn.CRT Latin / Crimean Tatar</div><div>
latn.DEU Latin / German</div><div>
latn.FRA Latin / French</div><div>
latn.ITA Latin / Italian</div><div>
latn.MOL Latin / Moldavian</div><div>
latn.ROM Latin / Romanian</div><div>
latn.TRK Latin / Turkish.</div><div></div>
Now, is there any way out? Can't 'locl' lookups have Greek as their language and 'ancient' as specification?
What are the linguistic alternatives allowed?
Comments
Obviously, this use of the tags has not really come to fruition, and instead there are more or less unreliable attempts to map the OTL language system tags to document language tagging, often via the same mechanisms used to specify spelling and hyphenation dictionaries.
The OTL language system tags for Greek are:
Whether those language system tags and associated features are accurately mapped from document language tagging in specific environments has to be tested on a case-by-case basis.