anchor.diff:      headless = base;
       demo = base // {
   
  -      buildInputs = [ makeWrapper ];
  +      buildInputs = [ makeWrapper libpulseaudio ];
   
         libPath = stdenv.lib.makeLibraryPath [
           alsaLib
  +        libpulseaudio
           libX11
           libXcursor
           libXinerama
  
positive.code:     the store using e.g.:
  
        releaseType=alpha
        version=0.16.51
        nix-prefetch-url file://$HOME/Downloads/factorio_\''${releaseType}_x64_\''${version}.tar.xz --name factorio_\''${releaseType}_x64-\''${version}.tar.xz
  
      Note the ultimate "_" is replaced with "-" in the --name arg!
  
negative.code:   binDists = {
      x86_64-linux = let bdist = bdistForArch { inUrl = "linux64"; inTar = "x64"; }; in {
        alpha = {
          stable        = bdist { sha256 = "1fg2wnia6anzya4m53jf2xqwwspvwskz3awdb3j0v3fzijps94wc"; version = "0.17.79"; withAuth = true; };
          experimental  = bdist { sha256 = "1fg2wnia6anzya4m53jf2xqwwspvwskz3awdb3j0v3fzijps94wc"; version = "0.17.79"; withAuth = true; };
        };
        headless = {
          stable        = bdist { sha256 = "1pr39nm23fj83jy272798gbl9003rgi4vgsi33f2iw3dk3x15kls"; version = "0.17.79"; };
          experimental  = bdist { sha256 = "1pr39nm23fj83jy272798gbl9003rgi4vgsi33f2iw3dk3x15kls"; version = "0.17.79"; };
        };
        demo = {
          stable        = bdist { sha256 = "07qknasaqvzl9vy1fglm7xmdi7ynhmslrb0a209fhbfs0s7qqlgi"; version = "0.17.79"; };
        };
      };
      i686-linux = let bdist = bdistForArch { inUrl = "linux32"; inTar = "i386"; }; in {
  