Given a regex and a datum, a regex engine yields whether the datum matches a pattern and, if a match was found, what matched.

给定一个正则表达式和数据，正则表达式引擎将得到数据是否匹配模式及匹配内容(如果找到匹配)等结果。

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Each browser's regex engine also has different internal optimizations.

每种浏览器的正则表达式引擎也有不同的内部优化。

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If all possible paths through the regex have been attempted but a match was not found, the regex engine goes back to step 2 to try again at the next character in the string.

如果正则表达式的所有可能路径都尝试过了，但是没有成功地匹配，那么正则表达式引擎回到第二步，从字符串的下一个字符重新尝试。

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If all possible paths through the regex have been attempted but a match was not found, the regex engine goes back to step 2 to try again at the next character in the string.

如果正则表达式的所有可能路径都尝试过了，但是没有成功地匹配，那么正则表达式引擎回到第二步，从字符串的下一个字符重新尝试。

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