>> […] lowercasing/uppercasing one character is context-dependent and
>> can result in more than one character: the uppercase of ß is SS.
>
> Actually, it is (or at least, can be, I don't want to start a
> fundamental discussion) ẞ.
But only in certain circumstances, like uppercased family names in
passports (e.g. Dreßen -> DREẞEN).
Werner