Fundamentally, the XRSpace is a position and an orientation, one that may change every frame.

getViewerPose() gets pose and view information for a viewer given an XR space.

However, the XR space has no inherent concept of a "view". When in immersive mode, aside from eye-level spaces, it doesn't quite make sense to request view data for the space since there's nothing telling you where the eyes are.

For example, what should getViewerPose(identity) return in immersive mode? Should it return just a single view? Should it return two views from the identity matrix, with the eyes offset based on device data? Which direction are the eyes offset in? Does this direction change as the viewer moves their head?