Method casefold

crates/vm/src/builtins/str.rs:706–719

(&self)

    // casefold is much more aggressive than lower
    #[pymethod]
    fn casefold(&self) -> Self {
        match self.as_str_kind() {
            PyKindStr::Ascii(s) => caseless::default_case_fold_str(s.as_str()).into(),
            PyKindStr::Utf8(s) => caseless::default_case_fold_str(s).into(),
            PyKindStr::Wtf8(w) => w
                .chunks()
                .map(|c| match c {
                    Wtf8Chunk::Utf8(s) => Wtf8Buf::from_string(caseless::default_case_fold_str(s)),
                    Wtf8Chunk::Surrogate(c) => Wtf8Buf::from(c),
                })
                .collect::<Wtf8Buf>()
                .into(),
        }
    }

    #[pymethod]
    fn upper(&self) -> Self {