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。
When a regex is put to use, the first step is to determine the position within the target string where the search should start.
与清单1相比，在清单1中，通过选择s： name子元素，就可以立即将查找结果限制为目标字符串。
Compare this to Listing 1 where the result of key lookup is immediately narrowed down to the desired string by selecting s: name children.
目标字符串很小时，这种方法只比正则表达式快一点，但更重要的是，字符串的长度不再影响执行测试所需要的时间。
This is just a bit faster than the regex-based test with small target strings, but, more importantly, the string's length no longer affects the time needed to perform the test.
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