code: func MaxExtension(d time.Duration) broker.SubscribeOption {
  	return func(o *broker.SubscribeOptions) {
  		if o.Context == nil {
  			o.Context = context.Background()
  		}
  
  		o.Context = context.WithValue(o.Context, maxExtensionKey{}, d)
  	}
  }
docs: // MaxExtension is the maximum period for which the Subscription should
  // automatically extend the ack deadline for each message.