The Server-side data validation
The Server-side data validation means utilizing PHP to verify if good values have been sent to the script. Using server-side validation has almost the exact opposite advantages and disadvantages of client-side development:
Yes, it is more secure and works perfectly with all browsers, but it does so at the expense of slightly higher server load and slower feedback for users.
One big advantage of server-side validation is that you can use PHP – a language in which you have already familiarized with by now.
PHP has a wide variety of functions and language features modify strings, check numbers are within ranges, and so on. In addition to this, you can use PHP to connect to a database to check whether a username exists, for example, which is obviously impossible using client-side scripting.