与就绪状态类似，responsetext属性的值在整个请求的生命周期中也会发生变化。
Like the ready state, the value of the responseText property changes throughout the request's life cycle.
生命周期类似于状态机的概念，在使用Studio时，可在UML中定义生命周期类。
Life cycles are analogous to the concept of state machines and when using Studio are defined in UML.
这有点类似于心电图上的波纹，波纹其实就记载着一个生命体在时间过程中的一种状态。
This is somewhat similar to the ripples on the ECG, the waves record the state of a living body in the course of time.
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