anchor.diff:  
     meta = {
       homepage = http://xmlsoft.org/;
  -    description = "A XML parsing library for C";
  +    description = "An XML parsing library for C";
       license = "bsd";
       platforms = stdenv.lib.platforms.linux;
       maintainers = [ stdenv.lib.maintainers.eelco ];
  
positive.code: { stdenv, fetchurl, zlib, python ? null, pythonSupport ? true }:
  
  assert pythonSupport -> python != null;
  
  
negative.code: 
    configureFlags = stdenv.lib.optionalString pythonSupport "--with-python=${python}";
  
    buildInputs = (stdenv.lib.optional pythonSupport [ 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.
      ++ (stdenv.lib.optional stdenv.isFreeBSD xz);
  
    propagatedBuildInputs = [ zlib ];
  
  