在这个特别的规则表达式中，出现了' [[：space：]] '字符类。
In this particular regular expression, we encounter the '[[: space:]]' character class.
可以将字符类看作是规则表达式的“原子”，通常会将那些原子组合成“分子”。
You can think of character classes as the "atoms" of regular expressions, and you will usually want to group those atoms into "molecules."
要记住AST类在包外是不可见的， 还有就是客户机（最终）只会传入它们想求值的表达式的一个字符串表示。
Remember that the AST classes aren't visible outside of this package at all and that clients will (eventually) simply pass in a String representation of the expression they want evaluated.
Pattern先保存要使用的表达式，然后将其传递给Matcher 类以便在字符序列的上下文中检查其匹配情况。
This expression is then retained by the Pattern class before it is passed on to the Matcher class to check for matches in the context of a character sequence.
如果你觉得字符串的.r转换方法不是很清晰，你也可以通过创建Regex类的实例来定义正则表达式，比如new Regex("""W""")。
Should you find the .r transformation method on strings unclear, you can also define regexes by creating new instances of the Regex class, as in: new Regex("""W""").
如果输出定义包含返回字符串的输出表达式，它们会生成VARGRAPHICS (255)forDB 2类型的列，或者基于数据库类型的等效列。
If the output definition contains output expressions returning a string, they produce columns of type VARGRAPHICS (255) for DB2, or an equivalent type depending on the database type.
元字符是正在表达式的本质，它是一类特殊的字符，下面展示了不同类型的元字符。
Metacharacters are special characters which are the essence of Regular Expressions. There are different types of metacharacters, described below.
当在派生类中重写时，返回由表达式编辑器表属性值组成的表达式字符串。
When overridden in a derived class, returns the expression string that is formed by the expression editor sheet property values.
当在派生类中重写时，返回由表达式编辑器表属性值组成的表达式字符串。
When overridden in a derived class, returns the expression string that is formed by the expression editor sheet property values.
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