anchor.diff:  
   let
     versionMajor = "0.6";
  -  versionMinor = "12";
  +  versionMinor = "13";
     version = "${versionMajor}.${versionMinor}";
   in
   stdenv.mkDerivation rec {
  
positive.code:   src = fetchurl {
      url = "mirror://gnome/sources/libcroco/${versionMajor}/${name}.tar.xz";
      hashOutput = false;
      sha256 = "ddc4b5546c9fb4280a5017e2707fbd4839034ed1aba5b7d4372212f34f84f860";
    };
  
    buildInputs = [
  
negative.code:   passthru = {
      srcVerification = fetchurl {
        failEarly = true;
        inherit (src) urls outputHash outputHashAlgo;
        fullOpts = {
          sha256Url = "https://download.gnome.org/sources/libcroco/${versionMajor}/"
            + "${name}.sha256sum";
        };
      };
    };
  
  