Seems kinda logical, since that’s how the Germans did it for a long time? ẞ wasn’t introduced until 2017 or so, AFAICT.
replyThat's in the standard. https://www.unicode.org/reports/tr21/tr21-5.html
reply[SpecialCasing] Contains additional case mappings that map to more than one character, such as "ß" to "SS".
5.1 adds uppercase ẞ which can fold to either ss or lowercase ß depending on the chosen algorithm.
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