What's configured here (see config/page_level/showcase-hero-image-swap.config.php):

• hero.media.type = 'collection' — the Hero hands the media slot to content.mediaCollection instead of content.image.
• hero.media.collection.presentation = 'swap' — three items crossfade automatically; each item is still rendered by content.image.
• hero.media.collection.items[].title/subtitle — the first two slides set their own heading/subheading, which swap in sync with the image; the third slide omits them and falls back to the static hero.title/hero.subtitle.
• hero.media.collection.behaviour.autoplay/interval/transition — a 4 second interval with a fade transition, no manual controls or indicators.
• hero.mediaPosition = 'background' — Hero's structural placement is unchanged; it doesn't know or care that multiple items are behind the scenes.

Still to review: carousel presentation (manual/drag navigation) is not implemented yet — only 'swap' renders today.