The open and close brackets ([and]) mark the beginning and end of the code block, respectively.

开方括号和闭方括号([和])分别标志代码块的开始和结束。

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At a rough level, you usually just want to automatically call a less specific rule at either the start or the end of execution of a code block.

在粗糙的层次上，您通常只想在开始或结束执行代码块时自动调用不太特定的规则。

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