def hs_indices(self):
        """tuple of (anchor_idx, addend_idxs) pair for each subtotal.

        Example::

            (
                (2, (0, 1, 2)),
                (3, (3,)),
                ('bottom', (4, 5))
            )

        Note that the `anchor_idx` item in the first position of each pair
        can be 'top' or 'bottom' as well as an int. The `addend_idxs` tuple
        will always contains at least one index (a subtotal with no addends
        is ignored).
        """
        if self.dimension_type in {DT.MR_CAT, DT.LOGICAL}:
            return ()

        return tuple(
            (subtotal.anchor_idx, subtotal.addend_idxs) for subtotal in self._subtotals
        )