CSharper

This is one of the powerful and useful validation control. These control perform validation based on the given resources in the form of expression. Expression or regular expression is a pattern of .NET provides System.Text.RegularExpressions namespace which contain many classes and methods to perform expression tasks .In ASP.NET regular expression validator control is provided which simplify the use of expression .ASP.NET provides regular expression editor which provides sample expression for use as well as for customization.
The Regular Expression Validator control allows you to check the value a user entered into a text box or other input control to ensure that it meets a particular form, such as a social security number, a phone number, and email address, etc.
         1. \d-digit
         2.\w-Character
         3.{}-Range of Character

        eg.1)PR123INV#123
      solution:-[A-Z a-z]{2}\d{3}[A-Z a-z]{3}#\d{3}                


Step 1)Drag and drop RegularExpressionValidator
Step 2)Go to properties window and first set ControlTovalidate as TextBox
Step 3)select another properties ValidationExpression and click.After clicking new window will open this windows is known as Regular Expression Editor and go to below Validation Expression and write
 \w{6,30}.means character range between 6 to 30.

Step 1:
                              save it,run and check out output.