. Any character
^ Start of subject
$ End of subject
[ Start character class definition
] End character class definition
| Start of alternative
( Start subpattern
) End subpatter
* 0 or more occurrences
+ 1 or more occurrences
? 0 or 1 occurrence
{ Start min/max quantifier
} End min/max quantifier
\ Escape character
\d Any decimal digit
\D Any character that is not a decimal digit
\s Any whitespace character
\S Any character that is not a whitespace character
\w Any "word" character
\W Any "non-word" character
\b Word boundary
\B Not a word boundary
$0 Full match
$1 First subpattern match
$2 Second subpattern match
$3 Third subpattern match
$4 4-th subpattern match
$5 5-th subpattern match
$6 6-th subpattern match
$7 7-th subpattern match
$8 8-th subpattern match
$9 9-th subpattern match