If I get it correctly, all QByteArray functions operate on Latin-1 encodings.

https://doc.qt.io/qt-5/qbytearray.html#8-bit-character-comparisons however states:

the notion of uppercase and lowercase[...] character is locale dependent

and to make the confusion perfect:

(If $LC_CTYPE is set, most Unix systems do "the right thing".)

I think this documenation should be changed to state that all these operations work for Latin1 encoding.