def changed(self):
        return set(o for o in self.intersect
                   if self.past_dict[o] != self.current_dict[o])
Initialization is identical to HighlightingDataCursor except for the
dataset/ETHPy150Open saltstack/salt/salt/states/cyg.py/DictDiffer.changed--crossover with--dataset/ETHPy150Open joferkington/mpldatacursor/examples/multi_highlight_example.py/MultiHighlight.__init__