 be considered a level reference, `key` must be a string that:
          - (axis=0): Matches the name of an index level and does NOT match
            a column label.
          - (axis=1): Matches the name of a column level and does NOT match
            an index label.

        Parameters
        ----------
        key : Hashable
            Potential level name for the given axis
        axis : int, default 0
            Axis that levels are associated with (0 for index, 1 for columns)

        Returns
        -------
        is_level : bool
        Nr