anchor.diff:  
     options = {
       services.zammad = {
  -      enable = lib.mkEnableOption "Zammad, a web-based, open source user support/ticketing solution.";
  -
  -      package = lib.mkOption {
  -        type = lib.types.package;
  +      enable = mkEnableOption "Zammad, a web-based, open source user support/ticketing solution.";
  +
  +      package = mkOption {
  +        type = types.package;
           default = pkgs.zammad;
  -        defaultText = "pkgs.zammad";
  +        defaultText = literalExpression "pkgs.zammad";
           description = "Zammad package to use.";
         };
   
  -      dataDir = lib.mkOption {
  -        type = lib.types.path;
  +      dataDir = mkOption {
  +        type = types.path;
           default = "/var/lib/zammad";
           description = ''
             Path to a folder that will contain Zammad working directory.
           '';
         };
   
  -      host = lib.mkOption {
  -        type = lib.types.str;
  +      host = mkOption {
  +        type = types.str;
           default = "127.0.0.1";
           example = "192.168.23.42";
           description = "Host address.";
         };
   
  -      port = lib.mkOption {
  -        type = lib.types.int;
  +      openPorts = mkOption {
  +        type = types.bool;
  +        default = false;
  +        description = "Whether to open firewall ports for Zammad";
  +      };
  +
  +      port = mkOption {
  +        type = types.port;
           default = 3000;
           description = "Web service port.";
         };
   
  -      websocketPort = lib.mkOption {
  -        type = lib.types.int;
  +      websocketPort = mkOption {
  +        type = types.port;
           default = 6042;
           description = "Websocket service port.";
         };
  
positive.code: { config, lib, pkgs, ... }:
  
  let
    cfg = config.services.zammad;
  
negative.code: 
    };
  
    config = mkIf cfg.enable {
  
      networking.firewall.allowedTCPPorts = mkIf cfg.openPorts [
        config.services.zammad.port
        config.services.zammad.websocketPort
      ];
  