anchor.diff:    passthru = {
       srcVerification = fetchurl rec {
         failEarly = true;
  -      urls = tarballUrls "1.2.10";
  +      urls = tarballUrls "1.2.11";
         pgpsigUrls = map (n: "${n}.asc") urls;
         pgpKeyFingerprint = "5ED4 6A67 21D3 6558 7791  E2AA 783F CD8E 58BC AFBA";
         inherit (src) outputHashAlgo;
  -      outputHash = "9612bf086047078ce3a1c154fc9052113fc1a2a97234a059da17a6299bd4dd32";
  +      outputHash = "4ff941449631ace0d4d203e3483be9dbc9da454084111f97ea0a2114e19bf066";
       };
     };
   
  
positive.code: 
    src = fetchurl {
      urls = tarballUrls version;
      multihash = "QmNdvd5s9vseKCdBQsHuk24B2XHnVNmyUziWQhetFPdroB";
      sha256 = "9612bf086047078ce3a1c154fc9052113fc1a2a97234a059da17a6299bd4dd32";
    };
  
    configureFlags = [
  
negative.code: assert static || shared;
  
  let
    version = "1.2.11";
  
    tarballUrls = version: [
      "http://zlib.net/zlib-${version}.tar.xz"
  