In addition, validation controls allow you to customize how error information is displayed to the user.
Validation controls provide an easy-to-use mechanism for all common types of standard validation—for example, testing for valid dates or values within a range—plus ways to provide custom-written validation.
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.
The regular expression is set in the Validation Expression property.
I'm sure that all the attributes of the controls makes sense by now, so I won't go into details about them. You should see something like this: If your browser supports Java Script, which most modern browers do, then you will notice that the page is not being posted back to the server - the validation is performed clientside! To see how it feels, you can add enableclientscript="false" to the Required Field Validator and try again.
Once it comes to serverside validation, it's your job to make sure that no sensitive code is executed unless you want it to.
As you see, it's very simple - just check the Page. Try to run the website again, and notice how the text of the button is changed if you submit a valid form.
Compares a user's entry against a constant value, against the value of another control (using a comparison operator such as less than, equal, or greater than), or for a specific data type.
For details, see Checks that the entry matches a pattern defined by a regular expression.