// tok must come from htmlcoarsetok
// returns all container tags found (including content) as CNC
// honors nested tags correctly
static L<L<S>> findContainerOrEmptyTag(L<S> tok, S tag) {
  new L<L<S>> l;
  for (int i = 1; i < l(tok); i += 2)
    if (isEmptyTag(tok.get(i), tag))
      l.add(tok.subList(i-1, i+1));
    else if (isOpeningTag(tok.get(i), tag)) {
      int j, level = 1;
      for (j = i+2; j < tok.size(); j += 2)
        if (isOpeningTag(tok.get(j), tag))
          ++level;
        else if (isTag(tok.get(j), "/" + tag)) {
          --level;
          if (level == 0) {
            l.add(tok.subList(i-1, j+2)); // actual CNC
            break;
          }
        }
      i = j;
    }
  ret l;
}