. for any character at all
\d for any digit;
\D for any non-digit
\s for any white space (including space, tab, newline, and return);
\S for any character that is not white space
x* to have zero or more x's;
(xy)* to have zero or more xy's
x? to have one or zero x's;
(xy)? to have one or no xy's
x+ to have one or more x's; (xy)+ to have one or more xy's
[abc] to include one of a group of values (a, b, or c)
[0–9] to include the range of values from 0 to 9
A|B to have A or B in the content.
x{5} to have exactly 5 x's (in a row)
x{5,} to have at least 5 x's (in a row)
x{5,8} to have at least 5 and at most 8 x's (in a row)
(xyz){2} to have exactly two xyz's (in a row).