You can assign a group name to a set of validators to ensure that validation occurs
only for controls in the specified group. This enables you to have multiple separately-validated
forms on a single page.
You can use the ValidationGroup property when you want to perform
separate validation tasks on the same page. In this example, the group name is assigned
to all the validator controls and the button that causes the validation.
By default, all validators are in the "" group (the default group) for backward
The page also exposes the GetValidators("group") and Validate("group")
methods. Page.IsValid reflects the validity of all controls (cumulative)
that have called the Validate method.