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. Examples of built-in root nodes include [AnimationNodeBlendTree] (allows blending nodes between each other using various modes), [AnimationNodeStateMachine] (allows to configure blending and transitions between nodes using a state machine pattern), [AnimationNodeBlendSpace2D] (allows linear blending between [b]three[/b] [AnimationNode]s), [AnimationNodeBlendSpace1D] (allows linear blending only between [b]two[/b] [AnimationNode]s).
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