| Character classes | 
                
                
                    | . | 
                    any character except newline | 
                
                
                    | \w \d \s | 
                    word, digit, whitespace | 
                
                
                    | \W \D \S | 
                    not word, digit, whitespace | 
                
                
                    | [abc] | 
                    any of a, b, or c | 
                
                
                    | [^abc] | 
                    not a, b, or c | 
                
                
                    | [a-g] | 
                    character between a & g | 
                
                
                    | Anchors | 
                
                
                    | ^abc$ | 
                    start / end of the string | 
                
                
                    | \b | 
                    word boundary | 
                
                
                    | Escaped characters | 
                
                
                    | \. \* \\ | 
                    escaped special characters | 
                
                
                    | \t \n \r | 
                    tab, linefeed, carriage return | 
                
                
                    | \u00A9 | 
                    unicode escaped © | 
                
                
                    | Groups & Lookaround | 
                
                
                    | (abc) | 
                    capture group | 
                
                
                    | \1 | 
                    backreference to group #1 | 
                
                
                    | (?:abc) | 
                    non-capturing group | 
                
                
                    | (?=abc) | 
                    positive lookahead | 
                
                
                    | (?!abc) | 
                    negative lookahead | 
                
                
                    | Quantifiers & Alternation | 
                
                
                    | a* a+ a? | 
                    0 or more, 1 or more, 0 or 1 | 
                
                
                    | a{5} a{2,} | 
                    exactly five, two or more | 
                
                
                    | a{1,3} | 
                    between one & three | 
                
                
                    | a+? a{2,}? | 
                    match as few as possible | 
                
                
                    | ab|cd | 
                    match ab or cd |