anchor.diff:  , x11grabExtlib ? false, libXext ? null, libXfixes ? null # X11 grabbing (legacy)
   , x264 ? null # H.264/AVC encoder
   , x265 ? null # H.265/HEVC encoder
  -, xavs ? null # AVS encoder
  +#, xavs ? null # AVS encoder
   , xvidcore ? null # Xvid encoder, native encoder exists
  -, zeromq4 ? null # Message passing
  +#, zeromq4 ? null # Message passing
   , zlib ? null
   #, zvbi ? null # Teletext support
   /*
  
positive.code:     #(mkFlag (libavc1394 != null) null null)
      (mkFlag (libbluray != null) "1.0" "libbluray")
      (mkFlag (libbs2b != null) "2.3" "libbs2b")
      (mkFlag (libcaca != null) "1.0" "libcaca")
      #(mkFlag (cdio-paranoia != null && gplLicensing) "0.9" "libcdio")
      (mkFlag (if !isLinux then false else libdc1394 != null && libraw1394 != null && isLinux) "0.5" "libdc1394")
      (mkFlag (libiconv != null) "1.2" "iconv")
  
negative.code:     (mkFlag (x11grabExtlib && gplLicensing) "0.5" "x11grab")
      (mkFlag (x264 != null && gplLicensing) "0.5" "libx264")
      (mkFlag (disDarwinFix (x265 != null && gplLicensing)) "2.2" "libx265")
      #(mkFlag (disDarwinFix (xavs != null && gplLicensing)) "0.7" "libxavs")
      (mkFlag (xvidcore != null && gplLicensing) "0.5" "libxvid")
      #(mkFlag (zeromq4 != null) "2.0" "libzmq")
      (mkFlag (zlib != null) "0.5" "zlib")
      #(mkFlag (zvbi != null && gplLicensing) "2.1" "libzvbi")
      /*
  