My C5 design law of cards: Cards contain content chunks and code.

“(…) when we talk about cards in digital products, it’s important to understand that there are actually two, interrelated concepts at work that some people conflate as one. I’ll use some grossly simplified language to label them as cards as presentation and cards as third-party content. (…) A card is a single unit of content or functionality, presented in a concise visual package. More advanced cards use that form to surface content or functionality from other apps, and allow users to interact with that content or functionality directly in the context of where a user encounters the card.”

(Khoi Vinh a.k.a. @khoi ~ Subtraction)