svoid phraseCache_mark(PhraseCache cache, LS tok, Set<Int> mark_io) {
  if (cache == null) ret;
  for (int i = 1; i < l(tok); i += 2) {
    L<LS> phrases = cache.byFirstWord.get(tok.get(i));
    new Best<LS> best;
    for (LS phrase : phrases)
      if (codeTokenSubListEqualsIC_skipFirst(tok, phrase, i))
        best.put(phrase, l(phrase));
    if (best.has()) {
      int j = i+l(best!)-3;
      while (i < j) {
        mark_io.add(i);
        i += 2;
      }
    }
  }
}