我的语法当其条件允许时找到了一个 ABC，但是当只能找到 A 或者 AB 时，也能满足于此。
My grammar finds an ABC when it is available, but settles for an A, or AB, when that is all there is to find.
元数据非常有用，因为它允许用户指定所有已检索文档必须满足的条件。
Metadata is helpful because it allows users to specify conditions that any retrieved document must meet.
PEP组件向PD p组件发送消息，询问是否满足策略中的条件，并根据结果允许过程继续或停止过程。
A PEP component sends a message to the PDP component asking if a condition in the policy is met, or not, in order to allow the process to continue, or stop the process.
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