The FreeBSD Ports Archive

 This module collects ip validation routines to make input validation, and
untainting easier and more readable.

All functions return an untainted value if the test passes, and undef if it
fails. This means that you should always check for a defined status
explicitly. Don't assume the return will be true. (e.g. is_username('0'))

The value to test is always the first (and often only) argument.