anchor.diff:    defaultHostTargetScope = pkgs // pkgs.xorg;
     defaultTargetTargetScope = pkgs.targetPackages // pkgs.targetPackages.xorg or {};
   
  -  splicer = pkgsBuildBuild: pkgsBuildHost: pkgsBuildTarget:
  -            pkgsHostHost: pkgsHostTarget:
  -            pkgsTargetTarget: let
  +  spliceReal = { pkgsBuildBuild, pkgsBuildHost, pkgsBuildTarget
  +               , pkgsHostHost, pkgsHostTarget
  +               , pkgsTargetTarget
  +               }: let
       mash =
         # Other pkgs sets
         pkgsBuildBuild // pkgsBuildTarget // pkgsHostHost // pkgsTargetTarget
  
positive.code:       in
          # The derivation along with its outputs, which we recur
          # on to splice them together.
          if lib.isDerivation defaultValue then augmentedValue // splicer
            (tryGetOutputs valueBuildBuild) (tryGetOutputs valueBuildHost) (tryGetOutputs valueBuildTarget)
            (tryGetOutputs valueHostHost) (getOutputs valueHostTarget)
            (tryGetOutputs valueTargetTarget)
          # Just recur on plain attrsets
          else if lib.isAttrs defaultValue then splicer
            valueBuildBuild valueBuildHost valueBuildTarget
            {} valueHostTarget
            valueTargetTarget
          # Don't be fancy about non-derivations. But we could have used used
          # `__functor__` for functions instead.
          else defaultValue;
      };
    in lib.listToAttrs (map merge (lib.attrNames mash));
  
    splicedPackages =
      if actuallySplice
      then
        splicer
          defaultBuildBuildScope defaultBuildHostScope defaultBuildTargetScope
          defaultHostHostScope defaultHostTargetScope
          defaultTargetTargetScope
        // {
          # These should never be spliced under any circumstances
          inherit (pkgs) pkgs buildPackages targetPackages
            buildPlatform targetPlatform hostPlatform;
        }
      else pkgs // pkgs.xorg;
  
  in
  
  {
    # We use `callPackage' to be able to omit function arguments that can be
    # obtained `pkgs` or `buildPackages` and their `xorg` package sets. Use
    # `newScope' for sets of packages in `pkgs' (see e.g. `gnome' below).
  
negative.code:         valueBuildBuild = pkgsBuildBuild.${name} or {};
          valueBuildHost = pkgsBuildHost.${name} or {};
          valueBuildTarget = pkgsBuildTarget.${name} or {};
          valueHostHost = throw "`valueHostHost` unimplemented: pass manually rather than relying on splice.";
          valueHostTarget = pkgsHostTarget.${name} or {};
          valueTargetTarget = pkgsTargetTarget.${name} or {};
          augmentedValue = defaultValue
  