anchor.diff:    config = {
   
       system.build.toplevel = stdenvNoCC.mkDerivation {
  -      name = "nixdarwin-system-${cfg.nixdarwinLabel}";
  +      name = "darwin-system-${cfg.darwinLabel}";
         preferLocalBuild = true;
   
         activationScript = cfg.activationScripts.script.text;
         activationUserScript = cfg.activationScripts.userScript.text;
  -      inherit (cfg) nixdarwinLabel;
  +      inherit (cfg) darwinLabel;
   
         buildCommand = ''
           mkdir $out
  
positive.code: 
          echo -n "$systemConfig" > $out/systemConfig
  
          echo -n "$nixdarwinLabel" > $out/nixdarwin-version
          echo -n "$system" > $out/system
        '';
      };
  
negative.code:       '';
      };
  
      system.darwinLabel = mkOption {
        type = types.str;
        default = pkgs.lib.nixpkgsVersion;
      };
  
    };
  