For anyone, like me, who isn't aware of what BridgeOS is... it is the apparent name for the iOS variant that will run on the A10 chip coming as part of the iMac Pro.
Thank you. I thought it was a book. It is not easy to figure out what it is.
At the bottom of the post is a link to volume 1 of a book about Apple Operating Systems, which presumably includes information about this new version of their operating system.