rating ``:hover`` tooltips.

        These string based tooltips are only applicable to ``<td>`` HTML elements,
        and cannot be used for column or index headers.

        .. versionadded:: 1.3.0

        Parameters
        ----------
        ttips : DataFrame
            DataFrame containing strings that will be translated to tooltips, mapped
            by identical column and index values that must exist on the underlying
            Styler data. None, NaN values, and empty strings will be ignored and
            not affect the rendered HTML.
        props : list-like or str, optional
            List of (attr, value) tuples or a valid CSS string. If ``None`` adopts
            the internal default values described in notes.
        css_class : str, optional
            Name of the tooltip class used in CSS, should conform to HTML standards.
            Only useful if integrating tooltips with external CSS. If ``None`` uses the
            internal default value 'pd-t'.

        Returns
        -------
        Styler

        Notes
        -----
        Tooltips are created by adding `<span class="pd-t"></span>` to each data cell
        and then manipulating the table level CSS to attach pseudo hover and pseudo
        after selectors to produce the required the results.

        The default properties for the tooltip CSS class are:

        - visibility: hidden
        - position: absolute
        - z-index: 1
        - background-color: black
        - color: white
        - transform: translate(-20px, -20px)

        The property 'visibility: hidden;' is a key prerequisite to the hover
        functionality, and should always be included in any manual properties
        specification, using the ``props`` argument.

        Tooltips are not designed to be efficient, and can add large amounts of
        additional HTML for larger tables, since they also require that ``cell_ids``
        is forced to `True`.

        Examples
        --------
        Basic application

        >>> df = pd.DataFrame(data=[[0, 1], [2, 3]])
        >>> ttips = pd.DataFrame(
        ...    data=[["Min", ""], [np.nan, "Max"]], columns=df.columns, index=df.index
        ... )
        >>> s = df.style.set_tooltips(ttips).to_html()

        Optionally controlling the tooltip visual display

        >>> df.style.set_tooltips(ttips, css_class='tt-add', props=[
        ...     ('visibility', 'hidden'),
        ...     ('position', 'absolute'),
        ...     ('z-index', 1)])  # doctest: +SKIP
        >>> df.style.set_tooltips(ttips, css_class='tt-add',
        ...     props='visibility:hidden; position:absolute; z-index:1;')
        ... # doctest: +SKIP
        z1Tooltips can only render with 'cell_ids' is True.z=Tooltips render only if `ttips` has unique index and columns.)