def tagged_to_same_mainstream_browse_page
      return [] unless content_item.parent

      @tagged_to_same_mainstream_browse_page ||= content_item.related_links.select do |related_item|
        related_item.mainstream_browse_pages.map(&:content_id).include?(content_item.parent.content_id)
      end
    end
def tagged_to_same_mainstream_browse_page
      return [] unless content_item.parent

      @tagged_to_same_mainstream_browse_page ||= content_item.related_links.select do |related_item|
        related_item.mainstream_browse_pages.map(&:content_id).include?(content_item.parent.content_id)
      end
    end
This will return related items that are tagged to the same mainstream
 browse page as the main content item.