+ ^%1,9in
%1,9in will try every combination of lowercase letters, uppercase letters, and digits, between 1 and 9 characters long.
If you want to try every possible ASCII character, then you would use %1,9q instead. This includes the full list of 95 printable ASCII characters (including lowercase, uppercase, digits, symbols, and space).
If you want to add line feeds, carriage return, and tabs, then instead use %1,9P.
If you want to expand beyond the 95 printable ASCII characters (such as to letters with diacritics or non-ASCII symbols), then you should use %1,9ic, and then specify all your custom characters using the command --custom-wild characters.
In terms of valid characters, you are looking at pretty much the full UTF-8 character set, which is thousands upon thousands of characters, including Greek and Cyrillic letters, CJK characters, mathematical operators, and even random symbols such as ⛄ and ⛅.