anchor.diff:      extraPackages = mkOption {
         default = pkgs: [];
         example = pkgs: [pkgs.firefox pkgs.thunderbird];
  +      merge = backwardPkgsFunListOldMerge;
         description = "
           This option allows you to add additional packages to the system
           path.  These packages are automatically available to all users,
  
positive.code:         packages.  The function will be called with the Nix Packages
          collection as its argument for convenience.
        ";
        merge = name: list:
          pkgsArg: pkgs.lib.concatMap (f: f pkgsArg) list;
      };
  
      nix = mkOption {
        default = pkgs: pkgs.nixUnstable;
        example = pkgs: pkgs.nixCustomFun /root/nix.tar.gz;
        description = "
          Use non-default Nix easily. Be careful, though, not to break everything.
        ";
  
negative.code: 
      extraFonts = mkOption {
        default = pkgs: [];
        merge = backwardPkgsFunListOldMerge;
        description = "
            Function, returning list of additional fonts.
        ";
  