The device element represents a complex node that includes an element with the name of the device and several other elements with additional information.
device元素表示一个复杂节点，它包含一个带有设备名称的元素和其他几个带有额外信息的元素。
Messages can be simple signals, complex combinations of node information, or conditional data.
消息可以是简单的信号、复杂的节点信息组合或者条件数据。
It is here, though, that a common question is asked: How do you write the query expression to get the correct node from an arbitrarily complex DOM?
但是，这里经常有人提问这样一个问题：如何编写查询表达式才能从任何复杂的DOM中获取正确的节点？
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