Let's refine our previous definition a little: "A validator is a control that checks one input control for a specific type of error condition and displays a description of that problem." This is an important definition, because it means that you frequently need to use more than one validator control for each input control.For example, if you want to check whether or not user input in a text box is (a) nonblank, (b) a valid date between a particular range and (c) less than the date in another text input control, you would want to use three validators.

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DTHML and scripting languages improve things somewhat.

It is possible to provide the user with immediate feedback on bad input and to prevent them from posting a page until it has been corrected.

Another element in our solution is the Validation Summary control.

Large data entry pages generally have an area where all errors are listed.

The user id must contain 6-10 alpha characters and must not already be in use.

The password must contain 4-12 letters and at least one of the characters "@#$%^&*/." The user must re-enter the password to make sure they entered it correctly.

For production applications, developers often end up spending a lot more time and code on this task than we would like. NET page framework, it was important to try and make the task of validating input a lot easer than it has been in the past.

In HTML 3.2, validating data is a difficult process.

If a client with Internet Explorer 4.0 or later uses your page, it can do the same input validation that takes place on the server without you having to write any special client script.

The client side validation has a number of features: In order to use validators effectively, it helps to have a firm definition of what they are.

Regular expressions can be very powerful in concisely expressing checks for this sort of information, as well as ZIP codes, phone numbers, and e-mail addresses.