Desc: an element containing a description of the service.
描述：包含服务描述的元素。
The key description is defined by desc, and its payload is pointed to by payload.
密钥描述由desc定义，它的有效内容由payload指定。
Because the desc attribute doesn't match the attribute named description, the value is not copied and the value is left unset.
因为desc属性不匹配名为description的属性，所以未复制并且未设置该值。
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