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Comment by dathinab | Hacker News Reader

Note that Unicode did add a "uppercase-ish" ß, as it does appear in German, but only in context of an all caps word e.g on a sign board, so captilazation of a whole word to SS and that new all caps ß are both correct (not sure if UNICODE changed the capitalization rules or just added that strange all caps ß)

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For backwards compatibility reasons, the capitalization rules can't be changed for existing characters. So normalizing by naive case-folding now requires at least three steps:

    "ẞ".to_lower() → "ß"
    "ß".to_upper() → "SS"
    "SS".to_lower() → "ss"

(there's a standard for how to compare strings case-insensitively that doesn't involve repeated case-folding, but it's much more complex)

Wow, I did not know about this weird edge case, interesting, thanks!

Unicode has a dedicated case folding[0][1] (as opposed to upper/lower case mapping) algorithm to cover these cases.

[0] https://www.unicode.org/reports/tr21/tr21-3.html#Caseless%20... [1] http://userguide.icu-project.org/transforms/casemappings#TOC...

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