code: def subject_areas(self):
          
          area = namedtuple('Area', 'area abbreviation code')
          path = ['subject-areas', 'subject-area']
          out = [area(area=item['$'], abbreviation=item['@abbrev'],
                      code=item['@code'])
                 for item in listify(chained_get(self._json, path, []))]
          return out or None
docs: List of namedtuples containing subject areas of the article
          in the form ().
          Note: Requires the FULL view of the article.