docs: def to_dictionary(self):
          """Serialize an object into dictionary form.  Useful if you have to
          serialize an array of objects into JSON.  Otherwise, if you call the
          :meth:`to_json` method on each object in the list and then try to
          dump the array, you end up with an array with one string."""
  
          d = {'start': self.start.isoformat(),
               'end': self.end.isoformat(),
               'tz': self.tz,
               'summary': self.summary.to_dictionary(),
               'series': self.series.to_dictionary()
               }
          return d