def _fmtos(self):
        """An iterator over formatoption objects

        Contains only the formatoption whose keys are in all plotters in this
        list"""
        plotters = self.plotters
        if len(plotters) == 0:
            return {}
        p0 = plotters[0]
        if len(plotters) == 1:
            return p0._fmtos
        return (getattr(p0, key) for key in set(p0).intersection(
            *map(set, plotters[1:])))