anchor.diff:  
         packageFun = mkOption {
           default = pkgs: pkgs.xorg;
  +        merge = backwardPkgsFunOldMerge;
           description = "
             Alternative X.org package to use. For 
             example, you can replace individual drivers.
  
positive.code:       description = ''
          A list of additional packages supplying kernel modules.
        '';
        merge = name: list:
          pkgsArg: pkgs.lib.concatMap (f: f pkgsArg) list;
      };
  
      kernelModules = mkOption {
  
negative.code:         packages.  The function will be called with the Nix Packages
          collection as its argument for convenience.
        ";
      };
  
      nix = mkOption {
        default = pkgs: pkgs.nixUnstable;
        example = pkgs: pkgs.nixCustomFun /root/nix.tar.gz;
        merge = backwardPkgsFunOldMerge;
        description = "
          Use non-default Nix easily. Be careful, though, not to break everything.
        ";
  