def METHOD_NAME(trees, notify):
    """ Handle keyword "items".
    Parameters
    ----------
    trees : list of lark.tree.Tree
        The children tree for the "items" rule.
        It should be empty.
    notify : bool
        True if the final target should notify, else False.
    Returns
    -------
    expression : ObserverExpression
    """
    if trees:
        # Nothing should be wrapped in items
        raise ValueError("Unexpected tree: {!r}".format(trees))
    return (
        expression_module.trait("items", notify=notify, optional=True)
        | expression_module.dict_items(notify=notify, optional=True)
        | expression_module.list_items(notify=notify, optional=True)
        | expression_module.set_items(notify=notify, optional=True)
    )