Admittedly, this property is a confusing one because it reads like a double negative, but by default, all read and unread documents are tracked in a database.
大家都认为这条属性令人费解，因为它读起来像是一个双重否定句，但是在默认情况下，数据库中所有已读的和未读的文档都会被跟踪。
The returned feed contains both read and unread items.
返回的内容中包含已读和未读的文章。
However, tracking read and unread documents has an impact on application performance.
然而，跟踪已读和未读文档会对应用程序的性能产生影响。
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