We deal with at least one form on almost every project. So we need to validate this form. You can do the validation with javascript on the client side. But we also need to validate on the server side because user can turn off the javascript.
To do the form validation on the server side, we need to understand about the regular expression.
Let's start with the simple example.
<?php
$string = "webinone";
echo preg_match("/in/",...
