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: 
  let
    inherit (pkgs.lib) mkOption;
  in
  
  {
  
negative.code:     kernelPackages = mkOption {
        default = pkgs: pkgs.kernelPackages;
        example = pkgs: pkgs.kernelPackages_2_6_25;
        merge = backwardPkgsFunOldMerge;
        description = "
          This option allows you to override the Linux kernel used by
          NixOS.  Since things like external kernel module packages are
  