regexp.txt

.           matches any character, except for line breaks if dotall is false
\w          matches any word character (alphanumeric and underscore) 
\W          matches any character that is not a word character (alphanumeric and underscore)
\d          matches any digit character (0-9)
\D          matches any character that is not a digit chracter (0-9)
\s          matches any whitespace character (spaces, tabs, line breaks)
\S          matches any character that is not a whitespace character (spaces, tagbs, line breaks)
[ABC]       matches any single character in the set
[^ABC]      matches any single character that is not in the set
[a-z]       matches any single character in the range of a-z
[a-zA-Z]    matches any single character in the range of a-z or A-Z
[^f-m]      matches any single character that is not in the range of f-m
[0-9]       matches any chracter in the range of 0-9
[\w'-]      matches any word character, single quote, or hyphen
\xFF        specify a character by its hexidecimal index (\xA9 matches the copyright symbol)
\\          matches a \ character
\.          matches a . character
\+          matches a + character
\*          matches a * cahracter
\?          matches a ? character
\^          matches a ^ character
\$          matches a $ character
\[          matches a [ character
\]          matches a ] character
\(          matches a ( character
\)          matches a ) cahracter
\|          matches a | character
\{          matches a { character
\}          matches a } character
\/          matches a / character
\'          matches a ' character
\#          matches a # chracter
\b          matches a word boundary position such as whitespace or the beginning or end of the string
\B          matches any position that is not a word boundary
^           matches the beginning of the string
$           matches trhe end of the string
(?=ABC)     positive look ahead. matches a group after your main expression without including it in the result
(?!ABC)     negative look ahead. specifies a group that can not match after your main expression (ie. if it matches the result is discarded)
(?<=ABC)    positive look behind. matches a group before your main expression without including it in the result
(?<!ABC)    negative look behind. specifies a group that can not match before your main expression (ie. if it matches the result is discarded)
?           make the preceeding token optional. It will match 0 or 1 of the preceeding token (colou?r matches both color and colour)
*           matches 0 or more of the preceeding token. This is a greedy match, and will match as many characters as possible before satisfying the next token
*?          matches 0 or more of the preceeding token. This is a lazy match, and will match as few characters as possible before satisfying the next token.
+           matches 1 or more of the preceeding token. This is a greedy match, and will match as many characters  as possible before satisfying the next token
+?          matches 0 or more of the preceeding token. This is a lazy match, and will match as few characters as possible before satisfying the next token
{5}         match exactly 5 of the preceeding token
{2, 5}      matches 2 to 5 of the preceeding token. This is a greedy match, and will match as many characters as possible before satisfying the next token
{2, 5}?     matches 2 to 5 of the preceeding token. This is a lazy match, and will match as few characters as possible before satisying the next token
(ABC)       group multiple tokens together. This allows you to apply quantifiers to the full group. This creates a capturing group
(?:ABC)     groups multiple tokens together without creating a capturing froup. This allows you to apply qauntifiers to the full group
|           alternation. Equivalent of "or". matches the full expression before or after the | (pear|kiwi|plum matches any pearl, kiwi, or plum)(cent(er|re) matches center or centre)
$$          an escaped $ symbol
$&          inserts the matched substring
$`          inserts the portion of the string the preceeds the match
$'          inserts the portion of the string that follows the match
$1          inserts the result of the first capture group


[0-9]+(?:\.[0-9]*)?     matches integer and decimal numbers
#?[0-9A-Fa-f]{6}        matches 24bit hex color values with ot without the leading #
\b0x(?:[0-9A-Fa-f]{6}|0-9A-Fa-f]{8})\b      matches 24bit or 32bit hex color values
<[^<]+?>                matches html tags
<?<=^|>)[^><]+?(?=<|$)  matches text that is not part of a html tag
([\w-\.]+)@((?:[\w]+\.)+)([a-zA-Z]{2,4})    matches email addresses