docs: def start_class(self, class_):
          """
          Start all services of a given class. If this manager doesn't already
          have a service of that class, it constructs one and starts it.
          """
          matches = filter(lambda svc: isinstance(svc, class_), self)
          if not matches:
              svc = class_()
              self.register(svc)
              matches = [svc]
          map(self.start, matches)
          return matches