web.ar interfaces.

The XR interface of the WebXR Device API provides methods for
an `web.ar.XRSession` object. Once a session is obtained, subsequent
or VR interactions with the hardware are done through it.

XR Events.

The XRFrame interface of the WebXR Device API provides information
to render a single frame of an AR/VR scene to the display. An
of this object is passed to each call of the callback provided
`XRSession.requestAnimationFrame`.

The XRInputSource interface of the WebXR Device API returns information
the Web AR/VR control device being used. The control device is
and defines a primary action. A primary action is a trigger,
button, spoken command, or hand gesture that when performed produces
`selectend`, and `select` events.

The XRSession of the WebXR Device API provides the means to interact
an AR/VR device, providing features such as polling the viewer
(viewer pose), getting information about the user's environment,
presenting imagery to the user. To get an XRSession call XR.requestSession().