static int gazelle_historyLevelRequired(RuleEngine2.Rule rule) {
  if (rule == null) ret 0;
  int n = 0;
  new Matches m;
  for (GRuleLine l : unnull(rule.insWithType))
    if (eq(l.type, "standard"))
      n = max(n, 1);
    else if (startsWith(l.type, "history-", m))
      n = max(n, parseIntOpt(m.rest()));
  ret n;
}