{4}matches exactly 4 characters from the set below:
A-Zone character from A (6510) to Z (9010) (case sensitive)
a-zone character from a (9710) to z (12210) (case sensitive)
0-9one character from 0 (4810) to 9 (5710)
Athe literal A (6510 / 1018 / 4116) (case sensitive)
@the literal @ (6410 / 1008 / 4016)
#the literal # (3510 / 438 / 2316)
\\the literal \ (9210 / 1348 / 5C16)
(the literal ( (4010 / 508 / 2816)