import org.eclipse.sapphire.ui.DragAndDropService;

public class ItemListDragAndDropService extends DragAndDropService {

    @Override
    public boolean droppable(DropContext context) {
        System.out.println("droppable");
        return false;
    }

    @Override
    public void drop(DropContext context) {
        System.out.println("drop");
    }
}

...
<case>
	<model-element-type>Itemlist</model-element-type>
	<label>[Itemlist] ... </label>
	<section>
		<label>Itemlist</label>
		<content>
                           <property-editor>
                               <service>
                                   <implementation>ItemListDragAndDropService</implementation>
                               </service>
                               <property>Item</property>
                           </property-editor>
		</content>
	</section>
</case>
...