正则表达式就是记录文本规则的代码。换句话说，在编写处理字符串的程序或网页时，经常会有查找符合某些复杂规则的字符串的需要。正则表达式就是用于描述这些规则的工具。(Regular expressions are code that records text rules. In other words, when writing programs or web pages dealing with strings, there is often a need to find strings that conform to certain complex rules. A regular expression is a tool for describing these rules.)