class_docstr: Creates ShapelyAnnotation (as shapely MultiPolygon).
  Can convert this instance annotation to various formats.
code: def multipolygon(self):
      return self.__multipolygon
  
imports: from typing import List
  from shapely.geometry import CAP_STYLE, JOIN_STYLE, MultiPolygon, Polygon, box
label_desc: Use image node_id 4 for calling the ShapelyAnnotation obj's underlying member method code with example usage: obj.multipolygon() and returns: self