Action is a type of node in Miarmy scene, and it's an asset of agent can drive the agent play animationsanimation (or sometimes we call it behavior)
The action should be created by an animated rig which the same rig used to generate the same type of Original Agent, that means one action belong to one type of agent.
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The action node not only contains the animation data, but also a full bunch of control data like loop, speed, etc
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The action node stores a clip of animation which can drive the agents to play concrete animation by logic trigger. And this is called behavior control.
And the action usually has a loop animation data, so once an agent play the action, it seems like entering a status.The action sometimes , and this is called behavior control
Also, the action can be a transition animation between 2 loop actions .like walk to stand