The Durable Layer
Skin and Skeleton: What Design Actually Owns
Nearly a decade ago, Alla Kholmatova split design systems into two kinds of pattern: functional patterns, the concrete parts like buttons and forms, and perceptual patterns, the expressive styles that carry personality, like color, type and motion (Design Systems, 2017). In an AI-generated world, that distinction becomes an ownership decision. Skeleton and Skin are my names for the two owners.
Functional Patterns
The Skeleton
Engineering-Owned
The component substrate: the library, its prop contracts and what actually ships. Any capable agent can read it and assemble it. It is plumbing: necessary, valuable and increasingly commoditized, because AI can generate a button.
- Lives in code, versioned in Git
- Prop contracts generated from code, not re-authored
- Swappable: MUI, Radix, in-house, whatever is next
Perceptual Patterns
The Skin
Design-Owned
The brand and identity system, meaning tokens plus brand rules. It is the layer that signals trust and makes a product recognizably itself. This is the invariant, and it is where design’s irreplaceable value concentrates.
- Portable across any substrate
- Tokens (DTCG format) plus structured brand logic
- The part a person has to stand behind
Front-end libraries churn: MUI, Radix, in-house, whatever is next. Bind a system’s identity to a specific substrate and it is fragile; the day engineering re-platforms, the design system re-platforms with it. A portable brand and identity layer survives that. It is the same principle I would apply anywhere a system has to outlast its parts: loose coupling, or architecting for failure, applied to the design system itself.
This is also where I stop trusting the marketing. Vendors say their tool is “the source of truth.” The useful question is never which tool. It is which field, owned by whom, enforced how. A tool that owns visual intent does not therefore own behavior, policy or shipped pixels. Read the architecture, not the announcement.
And one honest limit, because a credible model names them: this does not mean designers live inside a chat window. Working through Claude is right for generation and decision, the high-leverage judgment. But visual craft and exploration still want a canvas. The canvas does not disappear; its job narrows to exactly where human visual judgment actually lives.