Flags
i	make the pattern case insensitive
g	search for every occurence of the matching pattern
Position Characters
^	pattern must be at the start of the text string
$	pattern must be at the end of the text string
\b	match a position that is a word boundary (the point between a word character and a non-word character
\B	match a position that is not a word boundary
Character Classes
\d	match any digit 0-9
\D	match any character that is not a digit
\w	match any word character (0-9, A-Z, a-z, or _ )
\W	match any non-word character
\s	match any whitespace character (space, tab, newline, carriage return, form feed)
\S	match any non-whitespace character
.	match any character
Character Classes
[chars]	match any characters (chars) within the brackets
[^chars]	match any character except those within the brackets (chars)
[char1-charN]	match characters in the range char1 through charN
[^char1-charN]	do not match characters in the range char1 through charN
Repetition Characters
*	repeat zero or more times
?	repeat zero or one time
+	repeat one or more times
{n}	repeat exactly n times
{n, }	repeat at least n times
{n,m}	repeat at least n times, but no more than m times
Escape Sequences
\/	match a /
\\	match a \
\.	match a .
\*	match a *
\+	match a +
\?	match a ?
\|	match a |
\(	match a (
\)	match a )
\{	match a {
\}	match a }
\^	match a ^
\$	match a $
\n	match a new line
\r	match a carriage return
\t	match a tab
Alternative and Grouping Characters
chars1|chars2	match either the chars1 or chars2 character patterns
(chars)	group the character pattern char and treat it as a single unit. Matched groups are captured and available for later procession as back-reference
\n	the back-reference to group n
(?chars)	group the character pattern char and treat it as a single unit. Matched groups are not back-referenced