anchor.diff:    propagatedBuildInputs = [ findXMLCatalogs ];
   
     configureFlags = [
  -    "--with-libxml-prefix=${libxml2.dev}"
       "--without-debug"
       "--without-mem-debug"
       "--without-debugger"
  
positive.code: 
    outputs = [ "bin" "dev" "out" "man" "doc" ] ++ lib.optional pythonSupport "py";
  
    buildInputs = [ libxml2.dev ]
      ++ lib.optional stdenv.isDarwin gettext
      ++ lib.optionals pythonSupport [ libxml2.py python3 ]
  
negative.code: { lib, stdenv, fetchurl
  , pkg-config
  , libxml2, findXMLCatalogs, gettext, python3, libgcrypt
  , cryptoSupport ? false
  , pythonSupport ? stdenv.buildPlatform == stdenv.hostPlatform
  }:
  