No, we can't. The extender controls need to have a target control to extend; they don't work alone.
All the Extender controls have a property called TargetControlID, which indicates the control that the extender acts on.
The main advantage of the PopupControlExtender is it allows you to hide choices for a control within an UpdatePanel, saving valuable screen space.
We can use The Commit( )method is the method of the PopUpControlExtender that causes the target control to display the results .
From source view, we can set the WatermarkText property, but it's not visisble in the design view.