Paper

Composes with the classes `Box` computes instead of replacing them.

Which scale the `variant` paints with. Does nothing without a `variant`.

The element it paints. `article` or `section` when the sheet is a region of its own, so the elevation does not cost you the semantics.

Animates the element in when it first scrolls into view. `true` takes the catalogue entrance; an object tunes it — `preset`, `distance`, `spring`, `duration`, `once`, `amount`, `rootMargin` and `index` for a stagger. It lives here rather than on each surface so that `Card`, `Paper`, `GradientBorder`, `Section` and anything else built on `Box` inherit one implementation. Without it `Box` stays a server component; with it the root swaps for a client shell and the children keep rendering on the server. The entrance is a CSS transition, not a JavaScript animation: it is the only motion in the catalogue that fires WHILE the user scrolls, and the compositor should own it.

Elevation. It reads as height, so keep it consistent with what sits around: a sheet raised above its neighbours for no reason reads as an overlay.

The colour recipe, resolved against the theme's `variantMap` — so what `filled` or `glass` looks like is the theme's call, not the component's. Without it the sheet is the plain raised surface, which is the right default for a page.

Draws the edge. A `variant` that already brings its own border turns it on regardless, so this is only needed on the flat sheet.