SoGLViewingMatrixElement(3) on Linux
The text df985c8c22c4, as Debian 6.0 (Squeeze) shipped it.
The SoGLViewingMatrixElement class is used to store the current viewing matrix. The viewing matrix contains the inverse camera coordinate system matrix. The camera coordinate system is built from the field values in the current SoCamera (currently either SoPerspectiveCamera or SoOrthographicCamera) and any transformations prior to the camera in the scene graph.