static LS getHTMLComments(S html) {
  ret getHTMLComments(htmlTok(html));
}

static LS getHTMLComments(LS tok) {
  new LS l;
  for (int idx = 0; idx < l(tok); idx += 2) {
    S t = tok.get(idx);
    int i = 0;
    while ((i = indexOf(t, "<!--", i)) >= 0) {
      int j = smartIndexOf(t, "-->", i+4);
      l.add(substring(t, i+4, j));
      i = j+3;
    }
  }
  ret l;
}

Began life as a copy of #1008452