\ escape
^ match start (or negate group)
$ match end
. match any character (except newlines, [\s\S] to match newlines too)
[] match range (see examples below)
[^] negative match range, such as [^<]* (match up to but not including the next `<`)
\w, \W match any word character [a-zA-Z0-9_], NON-word character [^a-zA-Z0-9_]
\d, \W match any digit [0-9], NON-digit [^0-9]
\s, \S match any space [\t\v ], NON-space [^\t\v ] (also nbsp, etc, and \r\n in multiline mode... maybe)
\b match a word boundary (without capturing it), including start and end of line
+ match some (1+), such as \d+ (1 or more digits)
* match any (0+), such as .* (match all of anything)
? optional match (0 or 1)
{n,m} from n to m matches, such as \d{9,10} (match 9 or 10 digits - a phone number)
() capture group, such as (prefix)?(middle)(suffix)? matches prefixmiddle, middle, middlesuffix, prefixmiddlesuffix
| OR, such as (foo|bar)baz matches foobaz and barbaz
g find and replace all
m span multiple lines
/(foo)?(bar)(baz)?/gm
