anchor.diff:        ++ optional (vpxSupport && hasPrefix "0.8." version) ./vpxenc-0.8.17-libvpx-1.5.patch
         ;
   
  -    preConfigure = "patchShebangs doc/texi2pod.pl";
  +    postPatch = ''
  +      patchShebangs .
  +      # another shebang was hidden in a here document text
  +      substituteInPlace ./configure --replace "#! /bin/sh" "#!${bash}/bin/sh"
  +    '';
   
       configureFlags =
         assert stdenv.lib.all (x: x!=null) buildInputs;
  
positive.code:       ++ optional freetypeSupport "--enable-libfreetype"
        ;
  
    nativeBuildInputs = [ pkgconfig ];
      buildInputs = [ lame yasm zlib bzip2 SDL ]
        ++ [ perl ] # for install-man target
        ++ optional mp3Support lame
        ++ optional speexSupport speex
  
negative.code: { stdenv, fetchurl, pkgconfig, yasm, bzip2, zlib, perl, bash
  , mp3Support    ? true,   lame      ? null
  , speexSupport  ? true,   speex     ? null
  , theoraSupport ? true,   libtheora ? null
  