code: func (t *TextBar) HandleEvent(ev tcell.Event) bool {
  	switch ev.(type) {
  	case *EventWidgetContent:
  		t.changed = true
  		return true
  	}
  	return false
  }
docs: // HandleEvent handles incoming events.  The only events handled are
  // those for the Text objects; when those change, the TextBar adjusts
  // the layout to accommodate.