anchor.diff:            The upstream provider to use or custom in case you do not trust any of
             the predefined providers or just want to use your own.
   
  -          The default is ${defaultProvider} and there are privacy and security trade-offs
  -          when using any upstream provider. Please consider that before using any
  -          of them.
  +          The default is ${defaultProvider} and there are privacy and security
  +          trade-offs when using any upstream provider. Please consider that
  +          before using any of them.
   
  -          If you pick a custom provider, you will need to provide the bootstrap
  -          IP addresses as well as the resolver https URL.
  +          Supported providers: ${concatStringsSep ", " (builtins.attrNames providers)}
  +
  +          If you pick the custom provider, you will need to provide the
  +          bootstrap IP addresses as well as the resolver https URL.
           '';
  -        type = types.enum ((builtins.attrNames providers) ++ [ "custom" ]);
  +        type = types.enum (builtins.attrNames providers);
           default = defaultProvider;
         };
   
  
positive.code:   config = lib.mkIf cfg.enable {
      systemd.services.https-dns-proxy = {
        description = "DNS to DNS over HTTPS (DoH) proxy";
        after = [ "network.target" ];
        wantedBy = [ "multi-user.target" ];
        serviceConfig = rec {
          Type = "exec";
          DynamicUser = true;
          ExecStart = lib.concatStringsSep " " (
            [
              "${pkgs.https-dns-proxy}/bin/https_dns_proxy"
              "-a ${toString cfg.address}"
              "-p ${toString cfg.port}"
              "-l -"
  
negative.code:       ips = [ "9.9.9.9" "149.112.112.112" ];
        url = "https://dns.quad9.net/dns-query";
      };
      opendns = {
        ips = [ "208.67.222.222" "208.67.220.220" ];
        url = "https://doh.opendns.com/dns-query";
      };
      custom = {
        inherit (cfg.provider) ips url;
      };
    };
  
    defaultProvider = "quad9";
  
    providerCfg =
      concatStringsSep " " [
        "-b"
        (concatStringsSep "," providers."${cfg.provider.kind}".ips)
        "-r"
        providers."${cfg.provider.kind}".url
      ];
  
  in
  