3) MyEditDouble is "not" in the layout editor, because it doesn't have a .usc (visual representation) file at the moment. However, if you right click on the layout editor area, you'll see a menu item called "User Class" in the context menu. IF you select that item it will add a blank box, and let you set the class type (MyEditDouble) and its instance name on the left pane.

ctrl MyEditDouble {
	>EditDouble;
}