code: def sub_article_folders(self):
          
          l = list()
          for p in Path.sort_by_fname(
                  Path(self.dir_path).select_dir(recursive=False)
          ):
              af = ArticleFolder(dir_path=p.abspath)
              try:
                  if af.title is not None:
                      l.append(af)
              except:
                  pass
          return l
docs: Returns all valid ArticleFolder sitting inside of
          :attr:`ArticleFolder.dir_path`.