Character of regular expression, positional character and repeating character

Regular | repeat

Character classes represented by regular expression syntax
Character class	Matching characters	Example
\d	Numbers from the 0~9	\d\d can match 72, but cannot match 7a or A7
\d	Characters that are not numeric	\d\d\d can match a%c, but cannot match 123
\w	Underline and Word characters	\w\w\w can match a2_, but cannot match x&a
\w	Non-word characters and underscores	\w\w can match &^, but cannot match A1
\s	Blank characters, including tabs, line breaks, carriage returns, page breaks, and Vertical tabs
\s	Non-whitespace characters
.	Any character
[...]	Any character within the parentheses	[ABC] matches a single character a,b or C, but does not match other characters [A-z] matches any character of A~z
[^...]	Any character not in parentheses	[^ABC] matches any character that a,b,c out [A-z] matches any character that is not a~z, but matches large letters

positioning character
positioning character
^
$
\a
\z	The preceding pattern must be at the end of the string; The multiline flag is ignored
\z	< Font face= The preceding pattern must be at the end of the string, or before the newline character
\b< /font>
\b

repeat character	< Font face= "boldface" meaning	example
{n}		x{2} match xx, but does not match X, or xxx
{n,}		x{2, matches xx or xxx and more x,
{n, m}		x{2,4} matches Xx,xxx , XXXX but does not match X, or xxxxx
".	matches the preceding character 0 or 1 times/td>	x? Match x or null
+	matches the preceding characters 1 or more	x+ matches x or so many x
*		x* match empty or more x