Normally, the ControlDesigner.SetRegionContent(EditableDesignerRegion, string) method is not overridden in derived designers. The base class causes the design host to call the ControlDesigner.SetEditableDesignerRegionContent(EditableDesignerRegion, string) method for the region. Override the ControlDesigner.SetRegionContent(EditableDesignerRegion, string) method when custom data is required for the control before calling ControlDesigner.SetEditableDesignerRegionContent(EditableDesignerRegion, string) method.
Use the ControlDesigner.SetRegionContent(EditableDesignerRegion, string) method to insert HTML markup into a region of the control.