- Highlight range of test string that matches regex
- Highlight group in regex, when mouseover group match result
- beginnings of: Highlight range of test string that matches group, when
mouseover group match result
- Gray out "$n" label for unmatched groups (possible with ? or * quantifier, etc.)
- Fix bug: brace matching didn't ignore escaped parens since ( and \( were
both unstyled tokens. "Real" parens are now styled as "brace".
- Fix bug: "??" is a valid quantifier (non-greedy "?")
Highlight sample text matched by capturing group when mouseover the group
match UI - now truly, accurately detects the group matched text's pos in
most cases (and hopefully exits cleanly without highlighting anything in
the other cases).