这个赋值过程包含了给n1和n2赋值，然后将它们的值相加在一起，最后这个赋值的结果就是和。
the evaluation process consists of taking the values in the variables n1 and n2 and adding them together, and the result of the evaluation is whatever that sum happens to be.
如果库定义中提供了一种可视化模板，自动赋值过程将会被跳过，而 HTML 模板将会被评价，并由页面编辑器直接使用。
If a visualization pattern is provided in a library definition, the automatic rendering process will be bypassed, and the HTML pattern will be evaluated and used directly by the page editor.
告诉我们，接下来的赋值过程将使用异步的方式，而ReadAsync函数为BeginRead和EndRead方法如何被调用提供了规范。
"Tells us that the bind will be made asynchronously, and the ReadAsync function provides the specification of how the BeginRead and EndRead methods should be called."
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