static L<S> ocr_parseGroups(S s) {
  new L<S> l;
  for i over s:
    if (s.charAt(i) == '\\' && i+1 < l(s)) { // parse escaped character
      ++i;
      l.add(substring(s, i, i+1));
    } else if (s.charAt(i) == '[') { // parse group
      int j = i+1;
      new StringBuilder buf;
      while (j < l(s) && s.charAt(j) != ']') {
        if (s.charAt(j) == '\\' && j+1 < l(s)
          && eqOneOf(s.charAt(j+1), '[', ']')) ++j;
        buf.append(s.charAt(j++));
      }
      l.add(str(buf));
      i = j;
    } else
      l.add(substring(s, i, i+1));
  ret l;
}

Began life as a copy of #1006107