anchor.diff: -{ stdenv, fetchurl, zlib, xz, python, findXMLCatalogs }:
  +{ stdenv, lib, fetchurl, zlib, xz, python, findXMLCatalogs, libiconv
  +, supportPython ? (! stdenv ? cross) }:
   
   stdenv.mkDerivation rec {
     name = "libxml2-${version}";
  
positive.code:     moveToOutput share/man/man1 "$bin"
    '';
  
    passthru = { inherit version; pythonSupport = true; };
  
    meta = {
      homepage = http://xmlsoft.org/;
      description = "An XML parsing library for C";
      license = "bsd";
      platforms = stdenv.lib.platforms.unix;
      maintainers = [ stdenv.lib.maintainers.eelco ];
    };
  }
  
negative.code:     sha256 = "0bd17g6znn2r98gzpjppsqjg33iraky4px923j3k8kdl8qgy7sad";
    };
  
    outputs = [ "dev" "out" "bin" "doc" ]
      ++ lib.optional supportPython "py";
    propagatedBuildOutputs = "out bin" + lib.optionalString supportPython " py";
  
    buildInputs = lib.optional supportPython python
      # Libxml2 has an optional dependency on liblzma.  However, on impure
      # platforms, it may end up using that from /usr/lib, and thus lack a
      # RUNPATH for that, leading to undefined references for its users.
      ++ lib.optional stdenv.isFreeBSD xz;
  
    propagatedBuildInputs = [ zlib findXMLCatalogs ];
  
    configureFlags = lib.optional supportPython "--with-python=${python}";
  
    enableParallelBuilding = true;
  
    crossAttrs = lib.optionalAttrs (stdenv.cross.libc == "msvcrt") {
      # creating the DLL is broken ATM
      dontDisableStatic = true;
      configureFlags = configureFlags ++ [ "--disable-shared" ];
  
      # libiconv is a header dependency - propagating is enough
      propagatedBuildInputs =  [ findXMLCatalogs libiconv ];
    };
  
    preInstall = lib.optionalString supportPython
      ''substituteInPlace python/libxml2mod.la --replace "${python}" "$py"'';
    installFlags = lib.optionalString supportPython
      ''pythondir="$(py)/lib/${python.libPrefix}/site-packages"'';
  
    postFixup = ''
      moveToOutput bin/xml2-config "$dev"
  