. — any character
\d — digit [0-9]
\w — word char [a-zA-Z0-9_]
\s — whitespace
[abc] — char class
[^abc] — negated class
^ — start of string
$ — end of string
* — 0 or more
+ — 1 or more
? — 0 or 1
{n,m} — n to m times
(abc) — capture group
(?<name>) — named group
(?:abc) — non-capture
a|b — alternation