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.
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.
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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