The RegularExpressionValidator control is used to ensure that an input value matches a specified pattern.
Both server- and client-side validation are performed unless the browser does not support client-side validation or the EnableClientScript property is set to false.
The validation will not fail if the input control is empty. Use the RequiredFieldValidator control to make the field required.

Property:
BackColor  	The background color of the RegularExpressionValidator control
ControlToValidate 	The id of the control to validate
Display 	The display behavior for the validation control. Legal values are:

    * None (the control is not displayed. Used to show the error message only in the ValidationSummary control)
    * Static (the control displays an error message if validation fails. Space is reserved on the page for the message even if the input passes validation.
    * Dynamic (the control displays an error message if validation fails. Space is not reserved on the page for the message if the input passes validation

EnableClientScript 	A Boolean value that specifies whether client-side validation is enabled or not
Enabled 	A Boolean value that specifies whether the validation control is enabled or not
ErrorMessage 	The text to display in the ValidationSummary control when validation fails. Note: This text will also be displayed in the validation control if the Text property is not set
ForeColor 	The foreground color of the control
id 	A unique id for the control
IsValid 	A Boolean value that indicates whether the control specified by ControlToValidate is determined to be valid
runat 	Specifies that the control is a server control. Must be set to "server"
BackColor 	The background color of the RegularExpressionValidator control
Text 	The message to display when validation fails

ValidationExpression ::Specifies the expression used to validate input control. The expression validation syntax is different on the client than on the server. JScript is used on the client. On the server, the language you have specified is used