code: ComposeWarningsGuard makeEmergencyFailSafeGuard() {
      ComposeWarningsGuard safeGuard = new ComposeWarningsGuard();
      safeGuard.demoteErrors = true;
      for (WarningsGuard guard : guards.descendingSet()) {
        safeGuard.addGuard(guard);
      }
      return safeGuard;
    }
docs: Make a warnings guard that's the same as this one but demotes all
  errors to warnings.