code: func (c *CarouselContainer) MarshalJSON() ([]byte, error) {
  	return json.Marshal(&struct {
  		Type     FlexContainerType  `json:"type"`
  		Contents []*BubbleContainer `json:"contents"`
  	}{
  		Type:     FlexContainerTypeCarousel,
  		Contents: c.Contents,
  	})
  }
docs: // MarshalJSON method of CarouselContainer