Rust regex doesn't respect EcmaScript regex invalid pattern

[edgul]

The following test shows that this invalid regex input is being successfully parsed by Rust's Regex crate, but according to URLPattern spec it should fail.

 #[test]
  fn test_test() {
    let input = "((?R))"; // invalid in EcmaScript regex
    let _ = <UrlPattern>::parse(
      UrlPatternInit {
        protocol: Some(input.to_string()),
        ..Default::default()
      },
      Default::default(),
    )
    .unwrap();
  }

This currently passes because the following fragment passes:

    let input = "((?R))";
    let regexp = regex::Regex::new(input);
    regexp.unwrap();