PHP-Nuke 5.0 is on its way, and it is built almost from scratch. The worst news is that I am unaware of any HTML syntax checkers that can process PHP pages to check your work.

PHP’s enormous success, however, is not tied to specific tools. Rather, the combination of a code editor and a browser is likely the most common PHP development environment.

PHP can't "listen" because it's sent you the form and it's done, at least until you push the button that sends your POST. AJAX can do some listening for you, but that's not what an HTML form does.