[abx-z] One character of: a, b, or the range x-z

[^abx-z] One character except: a, b, or the range x-z

a|b a or b

a? Zero or one a's (greedy)

a?? Zero or one a's (lazy)

a* Zero or more a's (greedy)

a*? Zero or more a's (lazy)

a+ One or more a's (greedy)

a+? One or more a's (lazy)

a{4} Exactly 4 a's

a{4,8} Between (inclusive) 4 and 8 a's

a{9,} 9 or more a's

(?>...) An atomic group

(?=...) A positive lookahead

(?!...) A negative lookahead

(?<=...) A positive lookbehind

(?<!...) A negative lookbehind

(?:...) A non-capturing group

(...) A capturing group