The edge cases are hard to test. IIRC the weirdest issues had something to do with valid UTF-8 content the first X bytes of which also happened to be valid in s

The edge cases are hard to test. IIRC the weirdest issues had something to do with valid UTF-8 content the first X bytes of which also happened to be valid in some exotic charset related to the user's locale. English users would rarely come across such issues.