anchor.diff:  
   # java is problematic on some platforms, where it is unfree
   , enableJava ? true
  +
  +, buildPackages
   }:
   
   assert enableStandardFeatures ->
  
positive.code:     sha256 = "1clf1axkns23wfmh48xfspzsnw04pjh4mq1pshpzvj0cwxhz0yaq";
    };
  
    nativeBuildInputs = [ python3 unzip autoreconfHook ];
  
    # install filters early, so their shebangs are patched too
    postPatch = with lib; ''
  
negative.code:     # --replace "python3 -m asciidoc.a2x" "python3 -m asciidoc.a2x -a revdate=01/01/1980"
      substituteInPlace Makefile.in \
        --replace "python3 a2x.py" "python3 a2x.py -a revdate=01/01/1980"
    '' + lib.optionalString (stdenv.buildPlatform != stdenv.hostPlatform) ''
      # We want to use asciidoc from the build platform to build the documentation.
      substituteInPlace Makefile.in \
        --replace "python3 a2x.py" "python3 ${buildPackages.asciidoc}/bin/a2x.py"
    '';
  
    preInstall = "mkdir -p $out/etc/vim";
  