def register_gwf_format(container):
    """Register I/O methods for `format='gwf'`

    The created methods loop through the registered sub-formats.

    Parameters
    ----------
    container : `Series`, `dict`
        series class or series dict class to register
    """
    def read_(*args, **kwargs):
        fmt = 'gwf.{}'.format(get_default_gwf_api())
        reader = get_reader(fmt, container)
        return reader(*args, **kwargs)

    def write_(*args, **kwargs):
        fmt = 'gwf.{}'.format(get_default_gwf_api())
        writer = get_writer(fmt, container)
        return writer(*args, **kwargs)

    register_identifier('gwf', container, identify_gwf)
    register_reader('gwf', container, read_)
    register_writer('gwf', container, write_)