the key thing here is that if you know that no safe code contains invalid utf8, it is safe to do unsafe indexing into tables that are only sized to deal with va

the key thing here is that if you know that no safe code contains invalid utf8, it is safe to do unsafe indexing into tables that are only sized to deal with valid utf8. as such, this works in practice lead to ub in otherwise correct code, so it should be marked unsafe.