docs: 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:])))