anchor.diff:  let
     cfg = config.services.zabbixAgent;
   
  -  inherit (lib) mkDefault mkEnableOption mkIf mkOption;
  +  inherit (lib) mkDefault mkEnableOption mkIf mkMerge mkOption;
     inherit (lib) attrValues concatMapStringsSep literalExample optionalString types;
  +  inherit (lib.generators) toKeyValue;
   
     user = "zabbix-agent";
     group = "zabbix-agent";
  
positive.code:   # implementation
  
    config = mkIf cfg.enable {
  
      networking.firewall = mkIf cfg.openFirewall {
        allowedTCPPorts = [ cfg.listen.port ];
  
negative.code:         '';
        };
  
        settings = mkOption {
          type = with types; attrsOf (oneOf [ int str (listOf str) ]);
          default = {};
          description = ''
            Zabbix Agent configuration. Refer to
            <link xlink:href="https://www.zabbix.com/documentation/current/manual/appendix/config/zabbix_agentd"/>
            for details on supported values.
          '';
          example = {
            Hostname = "example.org";
            DebugLevel = 4;
          };
        };
  
      };
  