docs: def print_block(self, section_key, f=sys.stdout, file_format="mwtab"):
          """Print `mwtab` section into a file or stdout.
  
          :param str section_key: Section name.
          :param io.StringIO f: writable file-like stream.
          :param str file_format: Format to use: `mwtab` or `json`.
          :return: None
          :rtype: :py:obj:`None`
          """
          if file_format == "mwtab":
              for key, value in self[section_key].items():
                  if section_key == "METABOLOMICS WORKBENCH" and key not in ("VERSION", "CREATED_ON"):
                      continue
  
                  if key in ("VERSION", "CREATED_ON"):
                      cw = 20 - len(key)
                  elif key in ("SUBJECT_SAMPLE_FACTORS", ):
                      cw = 33 - len(key)
                  else:
                      cw = 30 - len(key)
  
                  if "\n" in value:
                      for line in value.split("\n"):
                          print("{}{}{}\t{}".format(self.prefixes.get(section_key, ""), key, cw * " ", line), file=f)
  
                  elif key == "SUBJECT_SAMPLE_FACTORS":
                      for factor in value:
                          print("{}{}\t{}".format(key, cw * " ", "\t".join(factor.values())), file=f)
  
                  elif key.endswith(":UNITS"):
                      print("{}\t{}".format(key, value), file=f)
  
                  elif key.endswith("_RESULTS_FILE"):
                      if isinstance(value, dict):
                          print("{}{}               \t{}\t{}:{}".format(self.prefixes.get(section_key, ""),
                                                                        *[i for pair in value.items() for i in pair]), file=f)
                      else:
                          print("{}{}{}\t{}".format(self.prefixes.get(section_key, ""), key, cw * " ", value), file=f)
  
                  elif key.endswith("_START"):
                      start_key = key
                      end_key = "{}{}".format(start_key[:-5], "END")
                      print(start_key, file=f)
  
                      for data_key in value:
                          if data_key in ("Samples", "Factors"):
                              print("{}\t{}".format(data_key, "\t".join(self[section_key][key][data_key])), file=f)
  
                          elif data_key in ("Fields", ):
                              print("{}".format("\t".join(self[section_key][key][data_key])), file=f)
  
                          elif data_key == "DATA":
                              for data in self[section_key][key][data_key]:
                                  print("\t".join(data.values()), file=f)
  
                      print(end_key, file=f)
                  else:
                      print("{}{}{}\t{}".format(self.prefixes.get(section_key, ""), key, cw * " ", value), file=f)
  
          elif file_format == "json":
              print(json.dumps(self[section_key], sort_keys=False, indent=4), file=f)