I need a vliadation for textbox
Codition is Either I can fill 7 numeric digit oR left null text box
<asp:TextBox runat="server" ID="txtmail" type="enroll" value="" placeholder="enroll"></asp:TextBox>
<asp:Button runat="server" ID="btnsubmit" type="submit" Text="Submit" value="Submit" />
Please help me.
Thanks