tions will always be plus
            or minus 90 degrees from level.

        use_clabeltext : bool, default: False
            If ``True``, use `.Text.set_transform_rotates_text` to ensure that
            label rotation is updated whenever the axes aspect changes.

        zorder : float or None, default: ``(2 + contour.get_zorder())``
            zorder of the contour labels.

        Returns
        -------
        labels
            A list of `.Text` instances for the labels.
        NF)