Dimensions

A version is not a second site. A locale is not a second site. They are coordinates on the same outline. dimensions() wraps N outlines (one per coordinate) into a single Outline that site() consumes. The coordinate is parsed off the front of the slug.

An axis over collections

You declare the axes, and a resolve that sources the outline for a coordinate. Versions are only collections. Give resolve the one that sources each:

import { site, dimensions } from 'ogygia/content';
import { v1, v2 } from './collections.server';

export const docs = site({
	base: '/docs',
	outline: dimensions({
		axes: { version: { values: ['v2', 'v1'], default: 'v2', label: 'Version' } },
		resolve: ({ version }) => (version === 'v1' ? v1 : v2)
	})
});
// /docs/routing        → v2 (the default serves bare)
// /docs/v1/routing     → v1

export const docs = site({
	base: '/docs',
	outline: dimensions({
		axes: {
			version: { values: ['v2', 'v1'], default: 'v2', label: 'Version' },
			locale: { values: ['en', 'de'], default: 'en', label: 'Language', fallback: true }
		},
		resolve: ({ version, locale }) => corpora[version][locale]
	})
});
// /docs/routing        → v2 × en
// /docs/de/routing     → v2 × de
// /docs/v1/de/routing  → v1 × de — the axes compose

The default coordinate serves at the bare URL. The others are prefixed. resolve is called one time per distinct coordinate, and memoized. Thus the outline of a version is built lazily, on the first visit.

Fallback, not 404

A missing translation is the common failure mode for versioned-docs sites. Dimensions handles it: an untranslated page renders the content of the default coordinate at its URL, and does not 404. The switcher can always link the same slug across coordinates, because the address is sure to resolve.

docs.page() reports what occurred on its fallback field. Thus the page can show a “not yet translated” note:

<script>
	const view = await docs.page(page.params.slug);
	// view.coordinate → { locale: 'de' };  view.fallback → { axis: 'locale', from: 'de', to: 'en' }
	// fallback is null when the page is native to its coordinate
</script>

{#if view.fallback}
	<aside>This page isn't translated to {view.fallback.from} yet — showing the {view.fallback.to} original.</aside>
{/if}

Fallback is per axis, opt-in (fallback: true on the axis). A locale usually wants it. A version usually does not: missing in v1 most frequently means did not exist yet, and that should 404.

The switcher

docs.switcher(slug) returns the version/locale picker for the coordinate in slug, with hrefs baked. It is a serializable value (one SwitcherAxis per axis) that the <Switcher> component renders as a dropdown. It stays on the same page across a switch. It lands on the equivalent of that page in the chosen coordinate (or the default, by the fallback rule).

You rarely call it directly. docs.meta(slug) bundles { nav, switcher, data } in one call, and <DocsShell {meta}> renders the switcher automatically when it is non-null.

Nav and search across the matrix

• nav(slug): pass the slug, so that the tree reflects that coordinate. The remote threads it through. A bare coordinate prefix like 'v1/' operates too.
• docs.entries(): bakes the union across the matrix. Thus a page that exists in only one coordinate still prerenders there.
• search: indexes only the canonical addresses of the default coordinate. Thus fallback pages under other coordinates do not show as duplicate hits.

Coordinate as data

The coordinate is threaded as data (slug → coordinate), never as module-global state. Thus it is SSR-safe under concurrent requests. You never reach for it directly. nav, page, switcher, and entries all take the slug and derive it.

Do / don’t

• Do model versions and locales as axes on one outline. One structure, read at coordinates, beats N parallel sites.
• Do rely on the fallback for locales. A missing translation should degrade to the default, never break the URL.
• Don’t encode the coordinate in module state. Pass the slug. The derivation is pure and request-safe.
• Don’t index each coordinate for search. The canonical set of the default is the honest result. Fallbacks are the same page.