A page can look calm while asking the system behind it to do quite a lot. A product option may change the image, price and information an order needs to retain.
Those details belong in the design conversation. We ask what the visitor should understand, which state the interface needs to show and what the person managing the site will receive.
That is the thought behind “surface and engine”: the visible experience and the behaviour that makes it possible need to agree.
See the product personalisation example
Studio observation / Updated October 2026