Special Characters
\			Escapes special characters or signals a special sequence.
.			Matches any single character except a newline.
^			Matches the start of the string.
$			Matches the end of the string.
*			Greedily matches 0 or more repetitions of the preceding RE.
*?			Matches 0 or more repetitions of the preceding RE.
+			Greedily matches 1 or more repetitions of the preceding RE.
+?			Matches 1 or more repetitions of the preceding RE.
?			Greedily matches 0 or 1 repetitions of the preceding RE.
??			Matches 0 or 1 repetitions of the preceding RE.
A|B			Matches A, if A is unmatched then matches B, where A and B are arbitrary REs.
{m}			Matches exactly m many repetitions of the previous RE.
{m,n}			Greedily matches from m many to n many repetitions of the previous RE.
{m,n}?			Matches m many to n many repetitions of the previous RE.

[...]			Indicates a set of characters to match.
[amk]			Matches 'a', 'm', or 'k'.
[a-z]			Matches 'a' through 'z'.
[a-f0-7]		Matches 'a' through 'f' or '0' through '7'.
[a\-z]			Matches 'a', '-', or 'z'.
[a-]			Matches 'a' or '-'.
[-a]			Matches 'a' or '-'.
[(+*)]			Matches '(', '+', '*', or ')'. [] matches special characters literally.
[\w]			Matches the character class for '\w'. See character classes.
[^5]			Matches anything other than '5'. '^' forms the complementary set only as the first character in a set.
[]()]			Matches ']', '(', and ')'. ']' is taken literally only as the first character in a set.
[()\]]			Matches ']', '(', and ')'.

(...)			Matches the RE inside the parenthesis and assigns a new group.
(?P<name>...)		The RE matched is accessible by the group indicated by name.

(?...)			Extension notation which changes a RE's behavior. These do not assign a new group.
(?aiLmsux)		Sets the corresponding flag to each letter. Does not work within Sublime Text.
(?:...)			A non-capturing version of parenthesis. The matched substring cannot be retrieved later.
(?P=name)		Matches the substring matched by the group named name.
(?#...)			A comment, the contents are ignored.
(?=...)			Lookahead assertion, the preceding RE only matches if this matches.
(?!...)			Negative lookahead assertion, the preceding RE only matches if this doesn't match.
(?<=...)		Positive lookbehind assertion, the following RE will only match if preceded with this fixed length RE.
(?<!...)		Negative lookbehind assertion, the following RE will only match if not preceded with this fixed length RE.
(?(id)true|false)	If group id exists then uses the true RE, else use the false RE.

Character classes
\1			Matches the contents of the group labelled by the same number. Acceptable numbers are 1-99.
\A			Matches at the start of the current string.
\b			Matches the empty string at the beginning or end of a word. \b matches the boundary between \w and \W.
\B			Matches the empty string not at the beginning or end of a word.
\d			Matches any Unicode decimal digit, including 0-9.
\D			Matches any Unicode non-decimal digit.
\s			Matches any Unicode whitespace character, including ' ', \t, \n, \r, \f and \v.
\S			Matches any Unicode non-whitespace character.
\w			Matches any Unicode word character, including a-z, A-Z, and 0-9.
\W			Matches any Unicode non-word character.
\Z			Matches at the end of the string.

\a			Matches the ASCII Bell ().
\f			Matches the ASCII Formfeed ().
\n			Matches the ASCII Linefeed.
\r			Matches the ASCII Carriage Return ().
\t			Matches the ASCII Horizontal Tab.
\v			Matches the ASCII Vertical Tab ().