Currently we are blocking 'immersive-ar' sessions from being created in favor of the non-standard 'legacy-inline-ar' mode. Creating an 'immersive-ar' mode session should transition the browser to display in fullscreen on a mobile device and begin compositing the camera feed behind the rendered content automatically. The XRSession.environmentBlendMode should be set to 'alpha-blend' when in this mode to indicate how content is being composited. Once enabled, the 'legacy-inline-ar' mode should be removed.