rited from the
            original Styler
          - ``css`` will be inherited from the original Styler, and the value of
            keys ``data``, ``row_heading`` and ``row`` will be prepended with
            ``foot0_``. If more concats are chained, their styles will be prepended
            with ``foot1_``, ''foot_2'', etc., and if a concatenated style have
            another concatanated style, the second style will be prepended with
            ``foot{parent}_foot{child}_``.

        A common use case is to concatenate user defined functions with
        ``DataFrame.agg`` or with described statistics via ``DataFrame.describe``.
        See examples.

        Examples
        --------
        A common use case is adding totals rows, or otherwise, via methods calculated
        in ``DataFrame.agg``.

        >>> df = DataFrame([[4, 6], [1, 9], [3, 4], [5, 5], [9,6]],
        ...                columns=["Mike", "Jim"],
        ...                index=["Mon", "Tue", "Wed", "Thurs", "Fri"])
        >>> styler = df.style.concat(df.agg(["sum"]).style)  # doctest: +SKIP

        .. figure:: ../../_static/style/footer_simple.png

        Since the concatenated object is a Styler the existing functionality can be
        used to conditionally format it as well as the original.

        >>> descriptors = df.agg(["sum", "mean", lambda s: s.dtype])
        >>> descriptors.index = ["Total", "Average", "dtype"]
        >>> other = (descriptors.style
        ...          .highlight_max(axis=1, subset=(["Total", "Average"], slice(None)))
        ...          .format(subset=("Average", slice(None)), precision=2, decimal=",")
        ...          .applymap(lambda v: "font-weight: bold;"))
        >>> styler = (df.style
        ...             .highlight_max(color="salmon")
        ...             .set_table_styles([{"selector": ".foot_row0",
        ...                                 "props": "border-top: 1px solid black;"}]))
        >>> styler.concat(other)  # doctest: +SKIP

        .. figure:: ../../_static/style/footer_extended.png

        When ``other`` has fewer index levels than the original Styler it is possible
        to extend the index in ``other``, with placeholder levels.

        >>> df = DataFrame([[1], [2]], index=pd.MultiIndex.from_product([[0], [1, 2]]))
        >>> descriptors = df.agg(["sum"])
        >>> descriptors.index = pd.MultiIndex.from_product([[""], descriptors.index])
        >>> df.style.concat(descriptors.style)  # doctest: +SKIP
        z `other` must be of type `Styler`z4`other.data` must have same columns as `Styler.data`zanumber of index levels must be same in `other` as in `Styler`. See documentation for suggestions.)