The format contains everything a Gerber File Set does, like images for all layers, drills, netlist, BOM. The information inside the ODB++ is strictly structured. Usually, there is no need to add anything, to fully and automatically define/understand the PCB and assembled components.
Thanks to included geometry data and netlist (the equivalent of IPC-356), ZofzPCB can create component models right from the start.
ODB++ feature is in the beta stage, starting with version 3.0.0.0.