anchor.diff:          '';
       };
   
  -    services.radvd.config = mkOption {
  +    package = mkOption {
  +      type = types.package;
  +      default = pkgs.radvd;
  +      defaultText = literalExpression "pkgs.radvd";
  +      description = ''
  +        The RADVD package to use for the RADVD service.
  +      '';
  +    };
  +
  +    config = mkOption {
         type = types.lines;
         example =
           ''
  
positive.code:         wantedBy = [ "multi-user.target" ];
          after = [ "network.target" ];
          serviceConfig =
            { ExecStart = "@${pkgs.radvd}/bin/radvd radvd -n -u radvd -C ${confFile}";
              Restart = "always";
            };
        };
  
negative.code: 
    ###### interface
  
    options.services.radvd = {
  
      enable = mkOption {
        type = types.bool;
        default = false;
        description =
  