docs: def addGraphic(self, typ='basic'):
          """
          Adds a new graphic to the scene.
          
          :param      typ | <str>
          
          :return     <XWalkthroughGraphic> || None
          """
          cls = XWalkthroughGraphic.find(typ)
          if not cls:
              return None
  
          graphic = cls()
          self.addItem(graphic)
          
          return graphic