docs: def bounds (self):
      """bounds() -> Rect
  
      Returns the bounding Rectangle for this Polygon.
      """
      if self._dirty:
        min = self.vertices[0].copy()
        max = self.vertices[0].copy()
        for point in self.vertices[1:]:
          if point.x < min.x: min.x = point.x
          if point.y < min.y: min.y = point.y
          if point.x > max.x: max.x = point.x
          if point.y > max.y: max.y = point.y
  
        self._bounds = Rect(min, max)
      self._dirty  = False
  
      return self._bounds