.Any char (not newline)\dDigit [0-9]\DNot digit\wWord char [a-zA-Z0-9_]\WNot word char\sWhitespace\SNot whitespace\bWord boundary^Start of string/line$End of string/line*0 or more+1 or more?0 or 1 (optional){n}Exactly n times{n,m}Between n and m[abc]Character class[^abc]Negated class(abc)Capture group(?:abc)Non-capture group(?=abc)Positive lookahead(?!abc)Negative lookahead(?<=abc)Positive lookbehinda|bAlternation (a or b)\1Backreference$1Replace group ref