Server side validation is performed by a web server, after input has been sent to the server.
Client side validation is performed by a web browser, before input is sent to a web server.
For example, here's what the page looks like if you forget to enter a course name, if you enter an, and if you enter an invalid date: By default, user input is validated after users submit the page — that is, the validation is performed in server code.
To see how validation works, run this page and deliberately make mistakes.
Client-based validation can also reduce the number of times that the user has to submit the form to correct multiple errors.
Note Even if you use client-side validation, validation is always also performed in server code.
However, the test will be performed in server code.
You can control how validation errors are displayed by defining CSS classes that have the following reserved names: .