code: def get_boundingbox(self):
          
          b = BoundingBox()
          for rx,rz in self.regionfiles.keys():
              region = self.get_region(rx,rz)
              rx,rz = 32*rx,32*rz
              for cc in region.get_chunk_coords():
                  x,z = (rx+cc['x'],rz+cc['z'])
                  b.expand(x,None,z)
          return b
docs: Return minimum and maximum x and z coordinates of the chunks that
          make up this world save