导出是该模块的一部分，它使组件对其他模块或应用程序可见。
An export is the part of the module that makes a component visible to other modules or applications.
普及服务仅对底层应用程序可见，即那些直接为服务编写的应用程序。
The pervasive services will be visible only to lower-level applications, i.e., those that write directly to services.
标记阶段负责跟踪应用程序可见的所有对象并将它们标记为活的，以免回收它们的存储。
The mark phase is responsible for tracing through all objects visible to the application and marking them as live to prevent them from having their storage reclaimed.
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