static LS toLines_nOnly_reversible(S s) {
  new LS lines;
  if (s == null) ret lines;
  int start = 0, n = s.length();
  while (true) {
    int i = indexOf(s, '\n', start);
    if (i < 0) {
      if (n > start) lines.add(s.substring(start));
      break;
    }

    lines.add(s.substring(start, i));
    ++i;

    start = i;
  }
  ret lines;
}