Ucamco published revision 2016.01 of the Gerber Format Specification. This revision adds new attributes for castellated holes (or PTH on the board edge) and for tooling and break-out holes.
The specification can be obtained from the download page of www.ucamco.com free of charge.
Ucamco (formerly Barco ETS) is a market leader in PCB CAM software, photoplotting and direct imaging systems, with a global network of sales and support centers. Headquartered in Ghent, Belgium, Ucamco has over 25 years of ongoing experience in developing and supporting leading-edge photoplotters and front-end tooling solutions for the global PCB industry. Key to this success is the company's uncompromising pursuit of engineering excellence in all its products. Ucamco also owns the IP rights on the Gerber File Format through its acquisition of Gerber Sytems Corp. (1998).