如果为零，这个例程返回并指出没有协议序列。

If so, then the routine simply returns saying that there are no protocol sequences.

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首先检查协议序列的数量是否为零。

The first check that is made is to see if the count of the protocol sequences is zero.

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从技术角度而言，正则表达式是表示某种模式的字符串(也就是说，由字母、数字和符号组成的字符序列)，用于定义零或更长的字符串。

Technically speaking, a regular expression is a string (that is, a sequence of characters composed of letters, Numbers, and symbols) that represents a pattern defining zero or more strings.

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