anchor.diff:  
     src = fetchurl {
       urls = tarballUrls version;
  -    multihash = "QmNzhnPYCnLukCSrycQNEkxJsghY9KP45cKeLqiKxxf6Ca";
  +    multihash = "QmZW6enUX5jA8JNCK72oQnCiaG4FEPuCHoC84yg12WyDqA";
       hashOutput = false;
  -    sha256 = "0b74e51595654f958148759cfef0993114ddccccbb6f31aee018f3558e8e2732";
  +    sha256 = "94fb70890143e3c6549f265cee93ec064c80a84c42ad0f23e85ee1fd6540a871";
     };
   
     buildInputs = [
  
positive.code: }:
  
  let
    version = "2.9.8";
  
    tarballUrls = version: [
      "http://xmlsoft.org/sources/libxml2-${version}.tar.gz"
  
negative.code:   passthru = {
      srcVerification = fetchurl rec {
        failEarly = true;
        urls = tarballUrls "2.9.9";
        inherit (src) outputHashAlgo;
        outputHash = "94fb70890143e3c6549f265cee93ec064c80a84c42ad0f23e85ee1fd6540a871";
        fullOpts = {
          pgpsigUrls = map (n: "${n}.asc") urls;
          pgpKeyFingerprint = "C744 15BA 7C9C 7F78 F02E  1DC3 4606 B8A5 DE95 BC1F";
        };
      };
    };
  
  