The BoundedPlane that was updated.
In a XRPlaneSubsystem.PlaneUpdated callback, this refers to an existing BoundedPlane previously detected in the physical world.
"Updated" generally means the understanding of the plane has changed, rather than tracking a change in the physical world.
For example, if the device's camera is able to see more of a particular surface, then it can provide an improved estimation of that surface.
However, if the surface itself moves, that would more likely be identified as a new surface rather than an update to an existing surface.
See Also: BoundedPlane, XRPlaneSubsystem