对于ESX，虚拟基础结构客户端软件将会选择这个mac地址，因此可以将其保留为空。

In the case of ESX, the virtual infrastructure client software chooses this MAC address, so it can be left blank.

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空 （用于浏览器和操作系统） 客户端的 DNS 缓存时 DNS 查找的数目是等于在网页上的唯一的主机名的数目。

When the client's DNS cache is empty (for both the browser and the operating system), the number of DNS lookups is equal to the number of unique hostnames in the web page.

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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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