code: def FieldData(self, field, Value = None):
          '''
          Add field data
          '''
          if Value == None:
              try:
                  return self.__FieldData[field]
              except KeyError:
                  return None
          else:
              if len(str(Value)) > self.__IsoSpec.MaxLength(field):
                  raise ValueError('Value length larger than field maximum ({0})'.format(self.__IsoSpec.MaxLength(field)))
              
              self.Field(field, Value=1)
              self.__FieldData[field] = Valuf FieldData(self, field, Value = None):
          '''
          Add field data
          '''
          if Value == None:
              try:
                  return self.__FieldData[field]
              except KeyError:
                  return None
          else:
              if len(str(Value)) > self.__IsoSpec.MaxLength(field):
                  raise ValueError('Value length larger than field maximum ({0})'.format(self.__IsoSpec.MaxLength(field)))
              
              self.Field(field, Value=1)
              self.__FieldData[field] = Value
docs: Add field data