这个消息键参数的值应是一个以逗号分隔的有效字符串列。
The value of the message-key parameter should be a comma-separated list of valid Strings.
大括号表示联合数组(即对象)，它的键-值组合由逗号分隔。
Curly braces denote an associative array (that is, an object), with its key-value pairs separated by commas.
JSON对象是由一个“键：值”对格式构成的，对象的元素由逗号隔开，每个对象包含在一对大括号中。
JSON objects are constructed in a key: value pair format. The elements of the object are separated by commas, and each object is contained within curly braces .
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