docs: def subjects(subjects=None,
               recursive=False,
               include_tables=False,
               lang=DEFAULT_LANGUAGE):
      """List subjects from the subject hierarchy.
  
      If subjects is not given, the root subjects will be used.
  
      Returns a generator.
      """
      request = Request('subjects', *subjects,
                        recursive=recursive,
                        includeTables=include_tables,
                        lang=lang)
  
      return (Subject(subject, lang=lang) for subject in request.json)