// i = index of opening tag
// returns index of closing tag + 1 (or -1 if no closing tag found)
static int findEndOfContainerTag(L<S> tok, int i) {
  S tag = getTag(tok.get(i));
  int j, level = 1;
  for (j = i+2; j < tok.size(); j += 2)
    if (isTag(tok.get(j), tag))
      ++level;
    else if (isTag(tok.get(j), "/" + tag)) {
      --level;
      if (level == 0)
        ret j+1;
    }
  ret -1;
}