An XRPose describing the state of a viewer of the XR scene as tracked by the XR
device. A viewer may represent a tracked piece of hardware, the observed position
of a user's head relative to the hardware, or some other means of computing a series
of viewpoints into the XR scene. XRViewerPoses can only be queried relative to an
XRReferenceSpace. It provides, in addition to the XRPose values, an array of views
which include rigid transforms to indicate the viewpoint and projection matrices.
These values should be used by the application when rendering a frame of an XR scene.
An XRPose describing the state of a viewer of the XR scene as tracked by the XR device. A viewer may represent a tracked piece of hardware, the observed position of a user's head relative to the hardware, or some other means of computing a series of viewpoints into the XR scene. XRViewerPoses can only be queried relative to an XRReferenceSpace. It provides, in addition to the XRPose values, an array of views which include rigid transforms to indicate the viewpoint and projection matrices. These values should be used by the application when rendering a frame of an XR scene.
ref: https://immersive-web.github.io/webxr/#xrviewerpose-interface