ASP.Net 2.0 client callback, first question

[Guest]

Hi all,
I am reading MSDN help to create my first client callback testing page.

From
ms-help://MS.VSCC.v80/MS.MSDN.v80/MS.VisualStudio.v80.en/dv_aspnetcon/html/dfaaa7d4-e1f2-4322-b2f5-796e0419f185.htm
I know I need to implement ICallbackEventHandler interface, and I checked
document, the return type of RaiseCallbackEvent defined in this interface is
void
(ms-help://MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref13/html/M_System_Web_UI_ICallbackEventHandler_RaiseCallbackEvent_1_16219e3a.htm),
but all the examples have something like

public String RaiseCallbackEvent(String eventArgument As String)
{
return eventArgument + " new value";
}

It is the samething in
ms-help://MS.VSCC.v80/MS.MSDN.v80/MS.VisualStudio.v80.en/dv_aspnetcon/html/2c688b1a-93a4-4dad-b82b-63974bdbb13e.htm

How is that possible?

Regards
Hardy