Opening up this specification allows those non-Intel employees to work on ambient light sensor support and hotkey-driven display output switching, among other features. IGD OpRegion is used on Intel IGPs in the 965 series and newer. Version 1.0 of this specification is 134 pages long.
Intel IGD OpRegion support had appeared in the Linux kernel back in August (kernel patch), but the documentation is finally being published today. The announcement was made on the X.Org mailing list and the specification can be downloaded from the Intel documentation page.