code: private boolean hasRuleSet(CssAtRule atRule, CssTokenIterator iter)
    {
      int debugIndex;
      if (debug)
      {
        checkArgument(iter.last.getChar() == '{');
        debugIndex = iter.index();
      }
      List<CssToken> list = iter.list;
      for (int i = iter.index() + 1; i < list.size(); i++)
      {
        CssToken tk = list.get(i);
        if (MATCH_OPENBRACE.apply(tk))
        {
          return true;
        }
        else if (MATCH_SEMI_CLOSEBRACE.apply(tk))
        {
          return false;
        }
      }
      if (debug)
      {
        checkState(iter.last.getChar() == '{');
        checkState(iter.index() == debugIndex);
      }
      return false;
    }
docs: With iter.last at '{', discover the at-rule type. The
  contents is a ruleset if '{' comes before ';' or '}'.