code: def birth_and_death_date2marc(self, key, value):
      
      name_field = self.get('100', {})
  
      if 'd' in name_field:
          if int(name_field['d'].split('-')[0]) > int(value.split('-')[0]):
              dates_field = ' - '.join([value, name_field['d']])
          else:
              dates_field = ' - '.join([name_field['d'], value])
      else:
          dates_field = value
  
      name_field['d'] = dates_field
  
      return name_field
docs: Populate the ``100__d`` MARC field, which includes the birth and the death date.
  
      By not using the decorator ```for_each_value```, the values of the fields
      ```birth_date``` and ```death_date``` are both added to ```values``` as a list.