可以通过将类括在方括号内来表明这是一个类；在括号中，可以有一组字符或者用破折号指定的字符范围。

You can indicate a class by surrounding it in square braces; within the braces, you can have both a set of characters and character ranges indicated with a dash.

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注意方括号(不是圆括号)中需要组成一个匿名列表引用。

Note the brackets (not parentheses), which are required to compose an anonymous list reference.

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注意：尖括号中的参数为可选参数；方括号()中的参数或选项为必需参数，必须提供。

Note: parameters shown in Angle brackets are optional; parameters or options shown in normal brackets () are required and must be provided.

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以上在方括号中显示的语法部分可以省去(在此情况下，必须将括号也省去)。

Parts of the above syntax shown in square brackets can be left out (in which case you have to leave the brackets out too).

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清单12还说明了DB 2中(方括号)和Oracle中(括号)中子索引的不同语法。

Listing 12 also illustrates the different syntax for sub-indexing in DB2 (square brackets) and in Oracle (parentheses).

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清单12还说明了DB 2中(方括号)和Oracle中(括号)中子索引的不同语法。

Listing 12 also illustrates the different syntax for sub-indexing in DB2 (square brackets) and in Oracle (parentheses).

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