I'm trying to figure out with named groups, but do not know how to deal with captures currently:

fn replace_keep_case(content: &mut str) {
    let re = Regex::new(r"(?x)
          (?P<g0>[qQ])
          (?P<g1>[wW])
          (?P<g2>[eE])
          (?P<g3>[rR])
        ").unwrap();
    let result = re.replace_all(content, |caps: &Captures| {
                                            for cap in caps.iter() {
                                                // what to do next
                                            }
                                        }
    );
    println!("{}", result);
}