'Add a commentary card.
If ``before`` and ``after`` are `None`, add to the last occurrence
of cards of the same name (except blank card).  If there is no
card (or blank card), append at the end.'

def _add_commentary(self, key, value, before=None, after=None):

    if ((before is not None) or (after is not None)):
        self._relativeinsert((key, value), before=before, after=after)
    else:
        self[key] = value
