Validating user input in php
I think "Beware a valid URL need not specify..." would be better.
FILTER_VALIDATE_EMAIL is discarding valid e-mail addresses containing IDN.
It's good to remember that using filter_var is primarily for filtering input values when doing boolean logic comparisons.
I was hoping I could get a quick scan to see if I'm doing things well or if it needs improvement.
Since there are real, live IDNs on the Internet, that means the filtered output is too strict, leading to false negatives.