https://www.rexegg.com/regex-quickstart.html#chars

CharacterLegendExampleSample Match
\d | Most engines: one digit
from 0 to 9 | file_\d\d | file_25
\d | .NET, Python 3: one Unicode digit in any script | file_\d\d | file_9੩
\w | Most engines: "word character": ASCII letter, digit or underscore | \w-\w\w\w | A-b_1
\w | .Python 3: "word character": Unicode letter, ideogram, digit, or underscore | \w-\w\w\w | 字-ま_۳
\w | .NET: "word character": Unicode letter, ideogram, digit, or connector | \w-\w\w\w | 字-ま‿۳
\s | Most engines: "whitespace character": space, tab, newline, carriage return, vertical tab | a\sb\sc | a b
c
\s | .NET, Python 3, JavaScript: "whitespace character": any Unicode separator | a\sb\sc | a b
c
\D | One character that is not a digit as defined by your engine's \d | \D\D\D | ABC
\W | One character that is not a word character as defined by your engine's \w | \W\W\W\W\W | *-+=)
\S | One character that is not a whitespace character as defined by your engine's \s | \S\S\S\S | Yoyo