\d - any number
\D - any non-digital character
\w - any letter
[abc123] - any character specified in square brackets
[abc123]? - any character specified in square brackets or the absence of a character
[abc123]+ - a sequence of any characters specified in square brackets
[abc123]* - the sequence of any characters specified in square brackets or the absence of a character
. - any character
.+ - an arbitrary sequence of any characters
.* - an arbitrary sequence of any characters or the absence of a character
b+ - arbitrary character sequence "b"
b* - an arbitrary sequence of the "b" character or its absence
\. - The dot symbol "."
.? - any symbol or its absence
b? - the "b" symbol or its absence
abc|xyz - one of the words (abc or xyz)
(abc) - the expression in parentheses is remembered for subsequent replacement (see the replacement options below)
^ - beginning of the line
$ - end of line