1. If this is the first time devices have been enumerated or |oldDevice| equals the [=immersive XR device=], abort these steps.

1. [=Shut down the session|Shut down=] any active {{XRSession}}s.

1. [=Queue a task=] to set the [=XR compatible=] boolean of all {{WebGLRenderingContextBase}} instances to `false`.

1. [=Queue a task=] to fire appropriate `change` events on any {{XRPermissionStatus}} objects who are affected by the change in the [=immersive XR device=] or [=/inline XR device=].

Note: These steps should always be run [=in parallel=].

The <dfn method for="XRSystem">isSessionSupported(|mode|)</dfn> method queries if a given |mode| may be supported by the user agent and device capabilities.

: If |limit| is `false` and the tracking system provides a [=6DoF=] pose whose position is actively tracked or statically known for |space|'s pose relative to |baseSpace|:

:: Set |transform|'s {{XRRigidTransform/orientation}} to the orientation of |space|'s [=effective origin=] in |baseSpace|'s [=coordinate system=].

:: Set |transform|'s {{XRRigidTransform/position}} to the position of |space|'s [=effective origin=] in |baseSpace|'s [=coordinate system=].

:: Set |pose|'s {{XRPose/emulatedPosition}} to `false`.

: Else if |limit| is `false` and the tracking system provides a [=3DoF=] pose or a [=6DoF=] pose whose position is neither actively tracked nor statically known for |space|'s pose relative to |baseSpace|:

:: Set |transform|'s {{XRRigidTransform/orientation}} to the orientation of |space|'s [=effective origin=] in |baseSpace|'s [=coordinate system=].

:: Set |transform|'s {{XRRigidTransform/position}} to the tracking system's best estimate of the position of |space|'s [=effective origin=] in |baseSpace|'s [=coordinate system=]. This MAY include a computed offset such as a neck or arm model. If a position estimate is not available, the last known position MUST be used.

:: Set |pose|'s {{XRPose/emulatedPosition}} to `true`.

: Else if |space|'s pose relative to |baseSpace| has been determined in the past and |force emulation| is `true`:

:: Set |transform|'s {{XRRigidTransform/position}} to the last known position of |space|'s [=effective origin=] in |baseSpace|'s [=coordinate system=].

:: Set |transform|'s {{XRRigidTransform/orientation}} to the last known orientation of |space|'s [=effective origin=] in |baseSpace|'s [=coordinate system=].

:: Set |pose|'s {{XRPose/emulatedPosition}} boolean to `true`.

: Otherwise:

[SecureContext, Exposed=Window] interface XRPose {

[SameObject] readonly attribute XRRigidTransform transform;

readonly attribute boolean emulatedPosition;

};

The <dfn attribute for="XRPose">transform</dfn> attribute describes the position and orientation relative to the base {{XRSpace}}.

The <dfn attribute for="XRPose">emulatedPosition</dfn> attribute is `false` when the {{XRPose/transform}} represents an actively tracked [=6DoF=] pose based on sensor readings, or `true` if its {{XRRigidTransform/position}} value includes a <dfn for="XRPose">computed offset</dfn>, such as that provided by a neck or arm model. [=Estimated floor level=]s MUST NOT be considered when determining if an {{XRPose}} includes a [=XRPose/computed offset=].

XRViewerPose {#xrviewerpose-interface}

Also, to prevent CORS-related vulnerabilities each [=browsing context=] will see a new instance of objects returned by the API, such as {{XRSession}}. Attributes such as the [=XRWebGLLayer/context=] set on an {{XRWebGLLayer}} with one [=relevant realm=] should not be able to be read through an {{XRWebGLLayer}} with a [=relevant realm=] that does not have the [=same origin=]. Similarly, methods invoked on the API MUST NOT cause an observable state change on other [=browsing contexts=]. For example: No method will be exposed that enables a system-level orientation reset, as this could be called repeatedly by a malicious page to prevent other pages from tracking properly. The user agent MUST, however, respect system-level orientation resets triggered by a user gesture or system menu.

Fingerprinting {#fingerprinting-security}

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Permissions Policy {#permissions-policy}

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The feature identifier for this feature is `"xr-spatial-tracking"`.