anchor.diff:          default = null;
           description = ''
             Your factorio.com login credentials. Required for games with visibility public.
  +        '';
  +      };
  +      package = mkOption {
  +        type = types.package;
  +        default = pkgs.factorio-headless;
  +        defaultText = "pkgs.factorio-headless";
  +        example = "pkgs.factorio-headless-experimental";
  +        description = ''
  +          Factorio version to use. This defaults to the stable channel.
           '';
         };
         password = mkOption {
  
positive.code:           Description of the game that will appear in the listing.
          '';
        };
        public = mkOption {
          type = types.bool;
          default = false;
  
negative.code: 
  let
    cfg = config.services.factorio;
    name = "Factorio";
    stateDir = "/var/lib/${cfg.stateDirName}";
    mkSavePath = name: "${stateDir}/saves/${name}.zip";
    configFile = pkgs.writeText "factorio.conf" ''
      use-system-read-write-data-directories=true
      [path]
      read-data=${cfg.package}/share/factorio/data
      write-data=${stateDir}
    '';
    serverSettings = {
  