[NTG-context] index sort order (de)

[Henning Hraban Ramm <texml@fiee.net>]

Hi,
I checked the German index sorting rules, and as far as I can tell, all 
of them are somewhat wrong.

– de, default, or no setting (just mainlanguage de)
– Duden
- DIN 5007-1(:2005)
- DIN 5007-2(:1996)
- de-AT

IMO, "Duden" is obsolete, should be the same as default; it makes no 
sense to have a default setting that doesn’t adhere to the official 
rules. If Û#m not mistaken it’s also the same as DIN 5007-1; maybe there 
was a difference before 2005. (DIN 5007-2 and de-AT have their uses.)

The order of umlauts etc. should be ok.

[ß]
In tex/context/base/mkiv/sort-lan.lua, ß is replaced by s, while it 
should be sorted like ss in default and both DIN versions. (de-AT sorts 
ss after ß.)

[upper-/lowercase]
While casing is not mentioned in Wikipedia 
(https://de.wikipedia.org/wiki/Alphabetische_Sortierung), Duden „Satz 
und Korrektur“ says:

Uppercase characters get sorted the same as lowercase (i.e. mixed), but 
if both appear, lowercase comes first.

ATM all German settings sort lowercase behind uppercase.



Generally, default method seems to be not "default" but "before". Does 
this make sense?

If we look at the method presets, there’s none for {zm,pm,zc,zm,uc} 
(upper like lower, ignore diacritics – basic default for German).

"""
\mainlanguage[de]
\setupregister[index][language=de]

\starttext

\index{Apfel}
\index{Äpfel}
\index{apfel}
\index{äpfel}
\index{aepfel}
\index{Aepfel}
\index{Ápfel}
\index{ápfel}

\page
\completeindex

\stoptext
"""

default order should be:

aepfel
Aepfel
apfel
Apfel
äpfel
Äpfel
ápfel
Ápfel
aqua

DIN 5007-2 sorts like:

aepfel
Aepfel
äpfel
Äpfel
apfel
Apfel
ápfel
Ápfel
aqua

de-AT sorts like:

aepfel
Aepfel
apfel
Apfel
aqua
äpfel
Äpfel
ápfel
Ápfel




Hraban
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