code: def _validate_item(self, validator, data_item, position, includes):
          
          errors = []
  
          # Optional field with optional value? Who cares.
          if data_item is None and validator.is_optional and validator.can_be_none:
              return errors
  
          errors += self._validate_primitive(validator, data_item, position)
  
          if errors:
              return errors
  
          if isinstance(validator, val.Include):
              errors += self._validate_include(validator, data_item,
                                               includes, position)
  
          elif isinstance(validator, (val.Map, val.List)):
              errors += self._validate_map_list(validator, data_item,
                                                includes, position)
  
          elif isinstance(validator, val.Any):
              errors += self._validate_any(validator, data_item,
                                           includes, position)
  
          return errors
docs: Validates a single data item against validator.
  
          Returns an array of errors.