code: def designspace(self):
          
          if self._designspace_is_complete:
              return self._designspace
  
          self._designspace_is_complete = True
          list(self.masters)  # Make sure that the UFOs are built
          self.to_designspace_axes()
          self.to_designspace_sources()
          self.to_designspace_instances()
          self.to_designspace_family_user_data()
  
          if self.bracket_layers:
              self._apply_bracket_layers()
  
          # append base style shared by all masters to designspace file name
          base_family = self.family_name or "Unnamed"
          base_style = find_base_style(self.font.masters)
          if base_style:
              base_style = "-" + base_style
          name = (base_family + base_style).replace(" ", "") + ".designspace"
          self.designspace.filename = name
  
          return self._designspace
docs: Get a designspace Document instance that links the masters together
          and holds instance data.