So let's look at the first subexpression.
因此，让我们研究一下第一个子表达式。
One such trick is the? : operator at the beginning of a subexpression.
其中一个技巧是子表达式开始处的？：运算符。
You can also refer to a subexpression from within a replacement string.
还可以从替换字符串中引用子表达式。
Parentheses in a regular expression are used to create a subexpression.
正则表达式中的括号用于创建子表达式。
Parentheses in a regular expression are used to create a subexpression.
正则表达式中的括号用于创建子表达式。
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