^ negation
- range
0123456789ABCDEF: specifies upper nybble. 8, therefore, means 0x80-0x8F
z: 0x00 character
a: a-zA-Z
b: 0x80-0xBF (all utf-8 continuers)
c: 0xC0-0xFE (all utf-8 starters)
d: 0-9
e: 0x1b, an escape sequence
f: 0xFF
n: newline
r: windows (0x0D==^M) line ending "announcer"
.,' : work just as the jokers in normal mode.
_: all special symbols that can be part of a valid variable name in the given language, except unicode characters. Usually, only '_' is contained. In C, '$' should be added, and in kubernetes, only '-' should be contained.