| Item | Purpose | 
        
            | \ | Either begins a special symbol such as \n or escapes the following character | 
        
            | ^ | Matches the beginning of string (or line if in multiline mode) | 
        
            | $ | Matches the end of string (or line if in multiline mode) | 
        
            | \A | Matches the beginning of string (even if in multiline mode) | 
        
            | \Z | Matches the end of string (even if in multiline mode) | 
        
            | * | Matches the preceding character zero or more times | 
        
            | + | Matches the preceding character one or more times | 
        
            | ? | Matches the preceding character zero or one time | 
        
            | . | Matches any character | 
        
            | [abc] | Matches any one of the characters inside the brackets | 
        
            | [^abc] | Matches one character that is not inside the brackets | 
        
            | [a-z] | Matches one character in the range of characters | 
        
            | [^a-z] | Matches one character that is not in the range of characters | 
        
            | x|y | Matches x or y | 
        
            | (pattern) | Makes a match group | 
        
            | (?<name>pattern) | Makes a match group and gives it a name | 
        
            | \n | Refers to a previously defined group | 
        
            | (?:pattern) | Make a non-capturing group (a group that you can't later refer to) | 
        
            | {n} | Matches exactly n occurrences | 
        
            | {n,} | Matches n or more occurrences | 
        
            | {n,m} | Matches between n and m occurrences | 
        
            | (?=...) | Positive lookahead (must match the pattern at this point) | 
        
            | (?!...) | Negative lookahead (must not match the pattern at this point) | 
        
            | (?<=...) | Positive lookbehind (the preceding text must match the pattern) | 
        
            | (?<!--...) | Negative lookbehind (the preceding text must not match the pattern) | 
        
            | \b | Matches a word boundary | 
        
            | \B | Matches a non-word boundary | 
        
            | \d | Matches a digit | 
        
            | \D | Matches a non-digit | 
        
            | \f | Matches a form-feed | 
        
            | \n | Matches a newline | 
        
            | \r | Matches a carriage return | 
        
            | \s | Matches white space (space, tab, form-feed, etc.) | 
        
            | \S | Matches non-white space | 
        
            | \t | Matches a tab | 
        
            | \v | Matches a vertical tab | 
        
            | \w | Matches a word character (includes underscore) | 
        
            | \W | Matches a non-word character |