these 2 derivations will be built:
  /nix/store/v99dbqywyqfcwblksdx7bykylzznyn18-unpack.drv
  /nix/store/q58y0hhrchfjrbb2a93sk1bndp9yylhc-facetimehd-firmware-1.43_5.drv
this path will be fetched (2.7 MiB download, 2.7 MiB unpacked):
  /nix/store/4l6pqyl0x5k2rjynijd6qxzfd91mn5fx-OSXUpd10.11.5.dmg