// tok must come from htmlTok
// returns all container tags found (including content) as CNC
// might not be correct with HTML sources
static L<L<S>> findContainerTags(L<S> tok) {
  new L<L<S>> l;
  for (int i = 1; i < l(tok); i += 2)
    if (isOpeningTag(tok.get(i))) {
      int j, level = 1;
      for (j = i+2; j < tok.size(); j += 2)
        if (isOpeningTag(tok.get(j)))
          ++level;
        else if (isClosingTag(tok.get(j))) {
          --level;
          if (level == 0) {
            l.add(subList(tok, i-1, j+2)); // actual CNC
            break;
          }
        }
      i = j;
    }
  ret l;
}