When a regex is put to use, the first step is to determine the position within the target string where the search should start.

当一个正则表达式投入使用时，首先要确定目标字符串中开始搜索的位置。

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As a regex works its way through a target string, it tests whether a match can be found at each position by stepping through the components in the regex from left to right.

当一个正则表达式扫描目标字符串时，它从左到右逐个扫描正则表达式的组成部分，在每个位置上测试能不能找到一个匹配。

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As a regex works its way through a target string, it tests whether a match can be found at each position by stepping through the components in the regex from left to right.

当一个正则表达式扫描目标字符串时，它从左到右逐个扫描正则表达式的组成部分，在每个位置上测试能不能找到一个匹配。

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