Look at the program:

  fn find_replaced_sequence_length(sequence: String) -> usize {
    // Replace the following patterns, one at a time:
    let substs = vec![
        ("tHa[Nt]", "<4>"),
        ("aND|caN|Ha[DS]|WaS", "<3>"),
        ("a[NSt]|BY", "<2>"),
        ("<[^>]*>", "|"),
        ("\\|[^|][^|]*\\|", "-"),
    ];
  
    // Perform the replacements in the sequence:
    substs
        .iter()
        .fold(sequence, |s, (re, replacement)| {
            regex(re)
                .replace_all(&s, NoExpand(replacement)).into_owned()
        }).len()
  }

It measures performance of RE engine. I can switch from regex crate to PCRE2, and program performance will match C.