After all of the validation controls have been called, a property on the page is set indicating whether any validation check has failed.Validation controls can be organized into groups that enable you to selectively enable or disable validation for related controls on a page.Other validation operations, such as displaying a method, can reference a specific validation group.
If the user is working with a browser that supports ECMAScript (Java Script), the validation controls can also perform validation using client script.
This can improve response time in the page because errors are detected immediately and error messages are displayed as soon as the user leaves the control containing the error. NET performs validation on the server even if the validation controls have already performed it on the client, so that you can test for validity within your server-based event handlers.
If a validation error is detected in any of the input controls, the page itself is set to an invalid state so you can test for validity before your code runs.
Validation occurs after page initialization (that is, after view state and postback data have been processed) but before any change or click event handlers are called.
However, if the control detects an error, it displays the error message text that you specify.