So, no Unicode or accented characters or even dots or hyphens? Your fellow Chinese, Korean, French, Swedish, Indian and Arabic Perlmonks will not be happy with that. Neither will your fellow Perl or C coders. (Nope, can't have Module.pm. Nor main.c. salary_run_2010-02? No payment for you!)
Sometimes, it's just easier to list what you want to exclude.
Comment on Re^3: Regular expression to check for invalid file name characters