code: def to_glyphs_family_user_data_from_designspace(self):
      
      target_user_data = self.font.userData
      for key, value in self.designspace.lib.items():
          if key == UFO2FT_FEATURE_WRITERS_KEY and value == DEFAULT_FEATURE_WRITERS:
              # if the designspace contains featureWriters settings that are the
              # same as glyphsLib default settings, there's no need to store them
              continue
          if _user_data_has_no_special_meaning(key):
              target_user_data[key] = value
docs: Set the GSFont userData from the designspace family-wide lib data.