anchor.diff:      optionalString;
   
     channel = "1.42";
  -  version = "${channel}.3";
  +  version = "${channel}.4";
   in
   stdenv.mkDerivation rec {
     name = "pango-${version}";
  
positive.code:   src = fetchurl {
      url = "mirror://gnome/sources/pango/${channel}/${name}.tar.xz";
      hashOutput = false;
      sha256 = "fb3d875305d5143f02cde5c72fec3903e60dc35844759dc14b2df4955b5dde3a";
    };
  
    nativeBuildInputs = [
  
negative.code:         outputHash
          outputHashAlgo
          urls;
        failEarly = true;
        fullOpts = {
          sha256Url = "https://download.gnome.org/sources/pango/${channel}/"
            + "${name}.sha256sum";
        };
      };
    };
  
  