Base class for Positional trackers managed by OpenXR's spatial entity extensions. These are trackers created and managed by OpenXR's spatial entity extensions that give access to specific data related to OpenXR's spatial entities. They will always be of type [code]TRACKER_ANCHOR[/code]. Adds a new [OpenXRStructureBase] to the next-chain. [method get_next] will return this [param next] until either [method add_next] is called again or it's removed in [method remove_next]. Gets the head [OpenXRStructureBase] in the next-chain. See also [method add_next] and [method remove_next]. Gets the spatial context used to create this [OpenXRSpatialEntityTracker]. Removes a [param next] object previously added in [method add_next] from the next-chain. Sets the spatial context used to create this tracker. The spatial entity associated with this tracker. The spatial tracking state for this tracker. Emitted when the next-chain changes, from either [method add_next] or [method remove_next]. This anchor has stopped tracking. Tracking is currently paused. This anchor is currently being tracked.