'The tr element next in sequence after the tr this cell appears in, or
|None| if this cell appears in the last row.'

@property
def _tr_below(self):

    tr_lst = self._tbl.tr_lst
    tr_idx = tr_lst.index(self._tr)
    try:
        return tr_lst[(tr_idx + 1)]
    except IndexError:
        return None
