A method that will handle the RichEditControl.CustomizeMergeFields event.
The event source.
A CustomizeMergeFieldsEventArgs object which contains event data.
When creating a CustomizeMergeFieldsEventHandler delegate, you identify the method that will handle the corresponding event. To associate an event with your event handler, add a delegate instance to this event. The event handler is called whenever the event occurs unless you remove the delegate. For more information about event handler delegates, see Events and Delegates in MSDN.