它标识消息且包含控制信息，比如消息类型和由发送应用程序分配的优先级。
It identifies the message and contains control information, such as the type of message and its priority as assigned by the sending application.
所有的流程控制变量(通常是布尔标识)都会以普通的基本变量类型来保存。
All the flow control variables (commonly Boolean flags) are stored as plain primitive types. As a high level rule I always say.
第一，使用名称空间作为标识和控制文档类型版本的一种方法。
The first is the use of namespaces as a method for identifying or versioning document types. You have likely seen the constructs such as.
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