Validation controls are associated with an input form field by using the ControlToValidate property of the validation control. This property must be set to the name/ID of the input field that we need to validate.
Sometimes you may have two independent forms that you want to validate but because the button control will trigger the validation process of all the controls in the page then you need to group only the controls that are meant to work with different buttons in a group
The normal behavior of a button is to send a form to a server for processing. Because of this buttons will usually trigger the validation controls on a page in order to make sure the form field input are validated before they are submitted to the server
This is used to compare a value in a form field to a regular expression. You can use it to check email address, postal codes, website address, social security number or any string patterns that you know how it is formatted.
We described the CompareValidator briefly in our previous video where we use it to compare the value a user has entered to a built-in Type such as Integer (we checked to see if user has entered whole number) otherwise they get error message
This control allows you to display all the validation errors on the page in one location. i explained in the previous videos that the ErrorMessage property is specifically for the ValidationSummary control and not for the validation control itself