可以将此处理程序部分内的信息绑定到UI内的变量，并将处理程序函数与在此UI内发生的其他事件关联起来。
You bind information in the handler part to variables within the UI, and associate handler functions with events that occur in the UI.
每个事件都在属于“当前”节点的转移函数的控制范围内，其中函数的范围是节点的一个子集。
Each event is in the domain of the transition function belonging to the "current" node, where the function's range is a subset of the nodes.
函数内的一些代码只有在某个事件触发或被调用的时候才会被执行。
A function contains some code that will be executed only by an event or by a call to that function.
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