anchor.diff:  
         enable = mkEnableOption "BIND domain name server";
   
  +
  +      package = mkOption {
  +        type = types.package;
  +        default = pkgs.bind;
  +        defaultText = "pkgs.bind";
  +        description = "The BIND package to use.";
  +      };
  +
         cacheNetworks = mkOption {
           default = [ "127.0.0.0/24" ];
           type = types.listOf types.str;
  
positive.code:       preStart = ''
          mkdir -m 0755 -p /etc/bind
          if ! [ -f "/etc/bind/rndc.key" ]; then
            ${pkgs.bind.out}/sbin/rndc-confgen -c /etc/bind/rndc.key -u ${bindUser} -a -A hmac-sha256 2>/dev/null
          fi
  
          ${pkgs.coreutils}/bin/mkdir -p /run/named
  
negative.code:       '';
  
        serviceConfig = {
          ExecStart = "${bindPkg.out}/sbin/named -u ${bindUser} ${optionalString cfg.ipv4Only "-4"} -c ${cfg.configFile} -f";
          ExecReload = "${bindPkg.out}/sbin/rndc -k '/etc/bind/rndc.key' reload";
          ExecStop = "${bindPkg.out}/sbin/rndc -k '/etc/bind/rndc.key' stop";
        };
  
        unitConfig.Documentation = "man:named(8)";
  