What is the format of a .xip file As Xcode 8 beta is available to download, I see it's distributed with a .xip extension, Xcode_8_beta.xip.

What is the .xip format? What's the difference between previous .dmg format?
According to the xip manual page:


  A XIP file is an analog to zip(1), but allows for a digital signature to be applied and verified on the receiving system, before the archive is expanded. When a XIP file is opened (by double-clicking), Archive Utility will automatically expand it (but only if the digital signature is intact).


Essentially, an .xip file is just a .zip with a signature to verify that the file has not changed since its creator saved it. This protects from both damage from a disk error and from a third-party tampering with the file.