Returns the position of the first substring match in a regular expression search.

返回正则表达式搜索中第一个子字符串匹配项的位置。

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You saw in Part 1, Figure 13 that the cn attribute type has a field called substr, which defines the matching rules for substring match.

在第1部分的图13可以看到，cn属性类型有一个叫做SUBSTR的字段，它定义了子字符串匹配的匹配规则。

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You need to search for a substring, and return either the starting position of the match or the matching value itself.

你想搜索一个字符串，获取该子字符串匹配的起始位置或匹配值。

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