Some frequently used predefined character classes are listed in the following Table.
| Predefined Character Classes | Meaning | Comments |
|---|---|---|
| . | Any character | may or may not match line terminators. |
| \d | A digit. | Same as [0-9] |
| \D | A non-digit. | Same as [^0-9] |
| \s | A whitespace character. | Same as [ \t\n\x0B\f\r]. The list includes a space, a tab, a new line, a vertical tab, a form feed, and a carriage return characters. |
| \S | A non-whitespace character. | Same as [^\s] |
| \w | A word character. | Same as [a-zA-Z_0-9]. The list includes lowercase letters, uppercase letter, underscore, and decimal digits. |
| \W | A non-word character. | Same as [^\w] |