The SDK's own tracking contract: what happened on the page, at the moments that count for tracking, named in the storefront style (product_added_to_cart, checkout_completed). Each carries the same object the SDK's events carry (the Cart, a CartItem, the Checkout, the Order), in one envelope: { event_id, event_type, object, data, created_at, session_id, sdk_version, context }. Each destination remaps them to its own format. next.analytics.on(name, (event) => …) receives one, '*' every one. How analytics works says how each is sent; each event's page has what triggers it, its data, and what each destination gets.