code: func (ww *WidgetWatchers) PostEventWidgetContent(w Widget) {
  	ev := &EventWidgetContent{}
  	ev.SetWidget(w)
  	ev.SetEventNow()
  	ww.PostEvent(ev)
  }
docs: // PostEventWidgetContent is called by the Widget when its content is
  // changed, delivering EventWidgetContent to all watchers.