In addition to what Graeme said, to have window with richedit and menu, it is usually better to actually avoid using layout and use MenuBar as frame.
struct MyEditorWindow {
MenuBar menu;
RichEdit edit;
.......
MyEditorWindow() {
Add(edit.SizePos()); // will fill entire view area
AddFrame(menu); // will be at the top, reducing the view area
.....
}
};