code: func Drag(xu *xgbutil.XUtil, grabwin xproto.Window, win xproto.Window,
  	buttonStr string, grab bool,
  	begin xgbutil.MouseDragBeginFun, step xgbutil.MouseDragFun,
  	end xgbutil.MouseDragFun) {
  
  	ButtonPressFun(
  		func(xu *xgbutil.XUtil, ev xevent.ButtonPressEvent) {
  			DragBegin(xu, ev, grabwin, win, begin, step, end)
  		}).Connect(xu, win, buttonStr, false, grab)
  
  	// If the grab win isn't the dummy, then setup event handlers for the
  	// grab window.
  	if grabwin != xu.Dummy() {
  		xevent.MotionNotifyFun(dragStep).Connect(xu, grabwin)
  		xevent.ButtonReleaseFun(DragEnd).Connect(xu, grabwin)
  	}
  }
docs: // Drag is the public interface that will make the appropriate connections
  // to register a drag event for three functions: the begin function, the
  // step function and the end function.
  // The 'grabwin' is the window that the grab is placed on (and therefore the
  // window where all button events are redirected to after the drag has started),
  // and the 'win' is the window that the initial 'begin' callback is set on.
  // In typical use cases, these windows should be the same.
  // If 'grab' is false, then no pointer grab is issued.