code: func (win *Window) GroupBegin(title string, flags WindowFlags) *Window {
  	sw := win.groupWnd[title]
  	if sw == nil {
  		sw = createWindow(win.ctx, title)
  		sw.parent = win
  		win.groupWnd[title] = sw
  		sw.Scrollbar.X = 0
  		sw.Scrollbar.Y = 0
  		sw.layout = &panel{}
  	}
  
  	sw.curNode = sw.rootNode
  	sw.widgets.reset()
  	sw.cmds.Reset()
  	sw.idx = win.idx
  
  	sw.cmds.Clip = win.cmds.Clip
  
  	state, bounds, _ := win.widget()
  	if !state {
  		return nil
  	}
  
  	flags |= windowSub | windowGroup
  
  	if win.flags&windowEnabled != 0 {
  		flags |= windowEnabled
  	}
  
  	sw.Bounds = bounds
  	sw.flags = flags
  
  	panelBegin(win.ctx, sw, title)
  
  	sw.layout.Offset = &sw.Scrollbar
  
  	win.usingSub = true
  
  	return sw
  }
docs: ///////////////////////////////////////////////////////////////////////////////////
  // GROUPS
  ///////////////////////////////////////////////////////////////////////////////////
  // Creates a group of widgets.
  // Group are useful for creating lists as well as splitting a main
  // window into tiled subwindows.
  // Items that you want to add to the group should be added to the
  // returned window.