code: def parse_preview(self, raw_content):
          
          if self._read_more_exp is None:
              return self.parse_whole(raw_content), False
  
          sp = self._read_more_exp.split(raw_content, maxsplit=1)
          if len(sp) == 2 and sp[0]:
              has_more_content = True
              result = sp[0].rstrip()
          else:
              has_more_content = False
              result = raw_content
          # since the preview part contains no read_more_sep,
          # we can safely use the parse_whole method
          return self.parse_whole(result), has_more_content
docs: Parse the preview part of the content,
          and return the parsed string and whether there is more content or not.
  
          If the preview part is equal to the whole part,
          the second element of the returned tuple will be False, else True.
  
          :param raw_content: raw content
          :return: tuple(parsed string, whether there is more content or not)