The delta file is a custom format created from the xar container format. It describes the necessary
modifications to transform the contents of the old directory in to the contents of the new. Binary
diffs are used to compress the differences between large files such as Mach-O binaries. The binary
diffs are generated by bsdiff and applied via bspatch, both from bsdiff 4.3, the source of which is
included and used under a BSD-style license.