A node to be used for advanced animation transitions in an [AnimationPlayer].
[b]Note:[/b] When linked with an [AnimationPlayer], several properties and methods of the corresponding [AnimationPlayer] will not function as expected. Playback and transitions should be handled using only the [AnimationTree] and its constituent [AnimationNode](s). The [AnimationPlayer] node should be used solely for adding, deleting, and editing animations.
Retrieve the motion of the [member root_motion_track] as a [Transform3D] that can be used elsewhere. If [member root_motion_track] is not a path to a track of type [constant Animation.TYPE_TRANSFORM3D], returns an identity transformation. See also [member root_motion_track] and [RootMotionView].
The path to the Animation track used for root motion. Paths must be valid scene-tree paths to a node, and must be specified starting from the parent node of the node that will reproduce the animation. To specify a track that controls properties or bones, append its name after the path, separated by [code]":"[/code]. For example, [code]"character/skeleton:ankle"[/code] or [code]"character/mesh:transform/local"[/code].
If the track has type [constant Animation.TYPE_TRANSFORM3D], the transformation will be cancelled visually, and the animation will appear to stay in place. See also [method get_root_motion_transform] and [RootMotionView].