N a person who is trained to provide basic life support in a medical emergency 第一急救者
Returns a Boolean value indicating whether the receiver is the first responder.
返回一个接收者是否是第一响应者的标识（布尔值）。
Notifies the receiver that it is about to become first responder in its window.
报告接受者它将要在 window 上成为为第一响应者。 默认返回 YES。
Any input is captured by the first responder, which tends to be the object that the user is directly interacting with.
任何输入都是由第一响应者先捕捉到的，它一般是与用户直接交互的对象。
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