尽量尝试将您的扩展函数设计为仅使用双精度、字符串、布尔和节点集作为实参和返回值的类型。

Try to design your extension functions so that they use only doubles, strings, booleans, and node-sets as both arguments and return values.

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要调用函数并使用它的返回值作为语言表达式的一部分，只需要命名它并附加一个使用圆括号括起的参数列表。

To call a function and use its return value as part of a larger expression, simply name it and append a parenthesized argument list.

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如果服务器端组件上的方法具有非空返回值，该值就会作为其惟一的实参传递进此回调函数。

If the method on the server-side component has a non-void return value, that value is passed into the callback function as its only argument.

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