code: def cast_item(cls, item):
          
          if not isinstance(item, cls.subtype):
              incompatible = isinstance(item, Base) and not any(
                  issubclass(cls.subtype, tag_type) and isinstance(item, tag_type)
                  for tag_type in cls.all_tags.values()
              )
              if incompatible:
                  raise IncompatibleItemType(item, cls.subtype)
  
              try:
                  return cls.subtype(item)
              except EndInstantiation:
                  raise ValueError('List tags without an explicit subtype must '
                                   'either be empty or instantiated with '
                                   'elements from which a subtype can be '
                                   'inferred') from None
              except (IncompatibleItemType, CastError):
                  raise
              except Exception as exc:
                  raise CastError(item, cls.subtype) from exc
          return item
docs: Cast list item to the appropriate tag type.