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Hi, First of all, my English is very bad, but I hope you will understand me. I started reading the chapter 11 (Ajax) and, at some points, I think that understood well, but there is one example that confuses me. Let's look at an example from the beginning of the book: I didn't really understand the purpose of this. If AJAX was used when user fills some fields like username, that would make sense. For example, when user enters username and onblur event happens - than AJAX will be used to "do the job" and that would save some time for that user if he entered username that already exists. And that makes sense. But, it this example, AJAX is used on submit. So, what the difference between using AJAX on submit and using some server script (<form ... action="script.php">) to validate data? In both cases, the user must press the button and see if he entered everything ok.