How can I declare and set values to the MaskedEditValidator using C#?

Hi!
I need to declare the MaskedEditValidator in C# so I can enter a value to the "Validationgroup" for this Ajax control using the code behind :

Protected System.......................??How I declare an Ajax control.....????........     MaskedEditValidator2;

I need to add this value to the attribute "ValidationGroup"  using C#:
    MaskedEditValidator2.ValidationGroup = "Group1";
Thanks

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<asp:MaskedEditValidator ID="MaskedEditValidator2" runat="server"  
        ControlToValidate="txtHiredPriorTo"  
        ControlExtender="MaskedEditExtender1"
        Display=Dynamic 
        ToolTip="Invalidate Date Format"  
        IsValidEmpty=false 
        EmptyValueMessage="Need to write a date" 
        InvalidValueMessage="This date is wrong"/>