code: def clipTo(self, bsp):
          
          self.polygons = bsp.clipPolygons(self.polygons)
          if self.front: 
              self.front.clipTo(bsp)
          if self.back: 
              self.back.clipTo(bsp)
docs: Remove all polygons in this BSP tree that are inside the other BSP tree
          `bsp`.