d of ``'<<='`` or ``'<<'``
    - ``warn_on_multiple_string_args_to_oneof`` - flag to enable warnings when :class:`one_of` is
      incorrectly called with multiple str arguments
    - ``enable_debug_on_named_expressions`` - flag to auto-enable debug on all subsequent
      calls to :class:`ParserElement.set_name`

    Diagnostics are enabled/disabled by calling :class:`enable_diag` and :class:`disable_diag`.
    All warnings can be enabled by calling :class:`enable_all_warnings`.
    r