| . | Any character (except newline unless s flag) |
| \w | Word character [a-zA-Z0-9_] |
| \W | Non-word character |
| \d | Digit [0-9] |
| \D | Non-digit |
| \s | Whitespace [ \t\n\r\f\v] |
| \S | Non-whitespace |
| \b | Word boundary |
| \B | Non-word boundary |
| ^ | Start of string / line (m flag) |
| $ | End of string / line (m flag) |
| * | 0 or more |
| + | 1 or more |
| ? | 0 or 1 (optional) |
| {n,m} | Quantifier: n to m times |
| (x) | Capturing group |
| (?:x) | Non-capturing group |
| (?=x) | Lookahead |
| (?!x) | Negative lookahead |
| (?<=x) | Lookbehind |
| (?<!x) | Negative lookbehind |
| [abc] | Character class |
| [^abc] | Negated character class |
| \| | Alternation (OR) |
| \1, \2... | Backreference |