Base class for [AnimationNode]s that hold one or multiple composite animations. Usually used for [member AnimationTree.tree_root].
[AnimationRootNode] is a base class for [AnimationNode]s that hold a complete animation. A complete animation refers to the output of an [AnimationNodeOutput] in an [AnimationNodeBlendTree] or the output of another [AnimationRootNode]. Used for [member AnimationTree.tree_root] or in other [AnimationRootNode]s.
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