Client-side validation of a control inside ASP.NET UserControl

I have created my ASP.NET UserControl which has a asp:DropDownList inside.

<asp:DropDownList ID="ddlExamYear" runat="server"></asp:DropDownList>

In a webpage, I add this UserControl to the page and also a RequiredFieldValidator to validate the control at page-level.

Actually, I can put the validation inside the control itself, but to make it flexible and general enough to use elsewhere, I decided to move the validation to the page-level instead.