code: def _check_content(self, content_str):
          
          if self.do_content_check:
              space_ratio = float(content_str.count(' '))/len(content_str)
              if space_ratio > self.max_space_ratio:
                  return "space-ratio: %f > %f" % (space_ratio,
                                                   self.max_space_ratio)
              if len(content_str) > self.input_character_limit:
                  return "too long: %d > %d" % (len(content_str),
                                                self.input_character_limit)
          return None
docs: Check if the content is likely to be successfully read.