AutoCompleteExtender in ASP.NET

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:AutoCompleteExtender ID="AutoCompleteExtender1" runat="server"
            TargetControlID="TextBox1" ServiceMethod="GetCompletionList"
            ServicePath="AjaxLearning.asmx" MinimumPrefixLength="1"
            CompletionListHighlightedItemCssClass="autocomplete_highlightedListItem"
            CompletionListItemCssClass="autocomplete_listItem"
            CompletionListCssClass="autocomplete_completionListElement"
            ShowOnlyCurrentWordInCompletionListItem="True">

        </asp:AutoCompleteExtender>