This method is intended for use by control developers who want to extend the UpdatePanel control. For example, in derived classes, you can provide a different root control that acts as a container for your UpdatePanel control's content. The default implementation returns a Control object.
The following example shows how to override the CreateContentTemplateContainer method in a custom UpdatePanel control to always render the <fieldset> and <legend> elements for the panel's content. The custom UpdatePanel control defines a public property named GroupingText that is a string literal inside the <legend> element.
A custom UpdatePanel control named CustomUpdatePanel derives from UpdatePanel and overrides the CreateContentTemplateContainer method. Put the CustomUpdatePanel class source code in the Web site's App_Code folder.