When using the react-transition-group library, what is the state of the transition?

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The react-transition-group library manages the state of the transition through the use of CSS classes. It adds CSS classes to the transitioning element during different stages of the transition, such as when it enters, leaves or is in the process of transitioning. These CSS classes can be customized to control the animation and appearance of the transition. The library also exposes lifecycle methods that can be used to manipulate the transition state programmatically.