anchor.diff:      ++ optional vaapiSupport       libva
       ++ optional drmSupport         libdrm
       ++ optional vapoursynthSupport vapoursynth
  +    ++ optional archiveSupport     libarchive
       ++ optionals dvdnavSupport     [ libdvdnav libdvdnav.libdvdread ]
       ++ optionals x11Support        [ libX11 libXext mesa libXxf86vm ]
       ++ optionals waylandSupport    [ wayland libxkbcommon ];
  
positive.code: , vaapiSupport       ? true,  libva         ? null
  , drmSupport         ? !stdenv.isDarwin,  libdrm        ? null
  , vapoursynthSupport ? false, vapoursynth   ? null
  , jackaudioSupport   ? false, libjack2      ? null
  
  # scripts you want to be loaded by default
  
negative.code: assert youtubeSupport     -> available youtube-dl;
  assert vapoursynthSupport -> available vapoursynth;
  assert jackaudioSupport   -> available libjack2;
  assert archiveSupport     -> available libarchive;
  assert vaapiSupport       -> available libva;
  assert drmSupport         -> available libdrm;
  
  