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| . | Any character (except newline, unless s flag) |
| \d \w \s | Digit · word char [A-Za-z0-9_] · whitespace |
| \D \W \S | Negated versions of the above |
| [abc] | Character set — any of a, b, c |
| [^abc] | Negated set — none of a, b, c |
| ^ $ | Start / end of string (or line with m flag) |
| \b \B | Word boundary / non-boundary |
| a* a+ a? | 0+ · 1+ · optional |
| a{n} a{n,} a{n,m} | Exactly n · n or more · between n and m |
| (abc) (?:abc) | Capturing group · non-capturing group |
| a|b | Alternation — a or b |
| (?<name>a) | Named capture group (use u flag recommended) |