Perl can help you understand this kind of thing on your own. I find YAPE::Regex::Explain handy for explaining "simple" regexes. Note that there is no support for regex syntax added after Perl version 5.6.

Win8 Strawberry 5.30.3.1 (64)  Thu 07/22/2021 20:17:20
C:\@Work\Perl\monks
>perl -wMstrict -MYAPE::Regex::Explain
-e "print YAPE::Regex::Explain->new(qr/^[\r\n\t -~]*$/s)->explain;"
The regular expression:

(?s-imx:^[\r\n\t -~]*$)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?s-imx:                 group, but do not capture (with . matching
                         \n) (case-sensitive) (with ^ and $ matching
                         normally) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  [\r\n\t -~]*             any character of: '\r' (carriage return),
                           '\n' (newline), '\t' (tab), ' ' to '~' (0
                           or more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

There are, of course, any number of on-line regex parsers, explainers and checkers, but I can't think of a good one ATM. Google is your friend.