message: tests: clarify numbered group binding
  This adds more tests to cover some corner cases in
  named/numbered group expansion.
  See also:
diff: @@ -92,7 +92,7 @@ pub fn expand_bytes(
  /// `CaptureRef` represents a reference to a capture group inside some text.
  /// The reference is either a capture group name or a number.
  ///
  -/// It is also tagged with the position in the text immediately proceeding the
  +/// It is also tagged with the position in the text following the
  /// capture reference.
  #[derive(Clone, Copy, Debug, Eq, PartialEq)]
  struct CaptureRef<'a> {
  @@ -204,6 +204,7 @@ mod tests {
  find!(find_cap_ref3, "$0", c!(0, 2));
  find!(find_cap_ref4, "$5", c!(5, 2));
  find!(find_cap_ref5, "$10", c!(10, 3));
  + // see https://github.com/rust-lang/regex/pull/585 for more on characters following numbers
  find!(find_cap_ref6, "$42a", c!("42a", 4));
  find!(find_cap_ref7, "${42}a", c!(42, 5));
  find!(find_cap_ref8, "${42");
  @@ -212,4 +213,8 @@ mod tests {
  find!(find_cap_ref11, "$");
  find!(find_cap_ref12, " ");
  find!(find_cap_ref13, "");
  + find!(find_cap_ref14, "$1-$2", c!(1,2));
  + find!(find_cap_ref15, "$1_$2", c!("1_",3));
  + find!(find_cap_ref16, "$x-$y", c!("x",2));
  + find!(find_cap_ref17, "$x_$y", c!("x_",3));
  }
  