code: func (win *Window) MenubarBegin() {
  	layout := win.layout
  
  	layout.Menu.X = layout.AtX
  	layout.Menu.Y = layout.Bounds.Y + layout.HeaderH
  	layout.Menu.W = layout.Width
  	layout.Menu.Offset = *layout.Offset
  	layout.Offset.Y = 0
  }
docs: // MenubarBegin adds a menubar to the current window.
  // A menubar is an area displayed at the top of the window that is unaffected by scrolling.
  // Remember to call MenubarEnd when you are done adding elements to the menubar.