docs: def _get_pdb_format_version(self):
          '''Remark 4 indicates the version of the PDB File Format used to generate the file.'''
          if not self.format_version:
              version = None
              version_lines = None
              try:
                  version_lines = [line for line in self.parsed_lines['REMARK'] if int(line[7:10]) == 4 and line[10:].strip()]
              except: pass
              if version_lines:
                  assert(len(version_lines) == 1)
                  version_line = version_lines[0]
                  version_regex = re.compile('.*?FORMAT V.(.*),')
                  mtch = version_regex.match(version_line)
                  if mtch and mtch.groups(0):
                      try:
                          version = float(mtch.groups(0)[0])
                      except:
                          pass
              self.format_version = version