Balloon popup Extender is used to provide a popup for the control when ever mouse pointer is over it  and whenever the control got the focus. Balloonpopup Extender has the following important properties.

TargetControlID:

Used to specify ID of the control to extend using the BallonpopupExtender.

BallonpopupControlID :

Used to specify ID of that control to popup, which is generally in panel.

BalloonStyle :

Used to specify the style of Balloon you want to popup the Balloon popup control

Position : Used to specify the position where you want to display the popup for the target control.

Balloon Size : Used to specify the size of the Balloon you want.

Display of Focus : Indicates whether or not popup is displayed when the focus is within the target contro.

Display on Mouse over : Indicates whether or not the popup is displayed whenever mouse pointer is over the target control.

Example 

The following example demonstrates how to use the Balloon popup extender.

Add a page to the web site and take a Toolkit script manger on it.

Take a text box & panel on the page, set ID of Text box T1 & within the panel provide some text that you want to provide as the popup for the textbox :

Within HTML source of the page Drag & drop a Ballon popup extender and set following properties to it.

<asp: Balloon Popup Extender ID=”Balloon Popup Extender1” runat=”server” TargetControlID = “T1” BalloonpopupcontrolID=”panel1” position=”TopRight” Balloon Style=”cloud” Display on focus =”false” BalloonSize = “small” DisplayonMouseover=”True”> </asp:Balloon popup Extender>

At runtime when you place the Mousepointer over the Textbox T1 Textbox T1 then the panel will pop up in cloud style at the top right of the Textbox T1.