SbViewportRegion(3) on Linux
The text 2491c2055ad7, as Debian 8 (Jessie) shipped it.
The SbViewportRegion class is a viewport within a full window. The SbViewportRegion class contains information to represent a subview within a window. It stores information about the origin and size of the subview, aswell as the size of the underlying 'full' window.