anchor.diff:  
     installPhase = ''
       for api in GL{,ES{,2,3},SC{,2}}; do
  -      pushd $api
  +      pushd $api/
           while read header; do
             install -D -m644 -v $header $out/include/$(basename "$api")/$header
           done < <(find . -name "*.h" -printf '%P\n')
         popd
  +    done
  +
  +    for xml in xml/*.xml; do
  +      install -D -m644 -v "$xml" \
  +        "$out"/share/opengl-registry/"$(basename "$xml")"
       done
     '';
   
  
positive.code: # TODO: build release tarballs, repo vendors pdfs
  
  let
    version = "2017-09-10";
  in
  stdenv.mkDerivation rec {
    name = "opengl-headers-${version}";
  
    src = fetchurl {
      url = "http://opengl-headers.tar.xz";  # dummy url
      multihash = "QmY1EgsrwD8RjC1S6AWavDUjKWZ1pAafovQb97FaFedM1G";
      sha256 = "f79976ac9731f02b515c2eef164443acdaf34cc6ad9e60a6165e50ac82bac5fe";
    };
  
    configurePhase = ":";
  
negative.code:       name = "opengl-headers-${version}";
  
        src = fetchFromGitHub {
          version = 6;
          owner = "KhronosGroup";
          repo = "OpenGL-Registry";
          rev = "68dba34a93b67d626b1c8b7294e4562bdaf4c996";
          sha256 = "6046f2eef181fe96379d23938de26e32621a59061d384b946db7e969bf16e99a";
        };
  
        nativeBuildInputs = [
  