static L<S> extractMarkedLines(S text, BitSet marking) {
  new L<S> l;
  L<Int> indexes = lineStartIndexes(text);
  for (int i : indexes) {
    int j = smartIndexOf(text, "\n", i);
    if (anyBitSetInRange(marking, i, j+1))
      l.add(substring(text, i, j));
  }
  ret l;
}