How to match “any character” in regular expression?

Question

The following should be matched:

AAA123
ABCDEFGH123
XXXX123

can I do: \".*123\" ?

Answer 1

The most common way I have seen to encode this is with a character class whose members form a partition of the set of all possible characters.

Usually people write that as [\s\S] (whitespace or non-whitespace), though [\w\W], [\d\D], etc. would all work.