diff --git a/packages/docs/src/App.tsx b/packages/docs/src/App.tsx
index b31e7dc..4217f81 100644
--- a/packages/docs/src/App.tsx
+++ b/packages/docs/src/App.tsx
@@ -13,6 +13,7 @@ import {
   basicRoutingDemoRoute,
   blogRoutingDemoRoute,
   dataGridDemoRoute,
+  complexRoutingDemoRoute,
   asyncLookupDemoRoute,
 } from "./router/routes";
 import Home from "./pages/Home";
@@ -24,6 +25,7 @@ import DemosIndex from "./pages/DemosIndex";
 import BasicRoutingDemo from "./pages/BasicRoutingDemo";
 import BlogRoutingDemo from "./pages/BlogRoutingDemo";
 import DataGridDemo from "./pages/DataGridDemo";
+import ComplexRoutingDemo from "./pages/ComplexRoutingDemo";
 import AsyncLookupDemo from "./pages/AsyncLookupDemo";
 import NotFound from "./pages/NotFound";
 
@@ -67,6 +69,9 @@ export const App = () => (
         <Route on={dataGridDemoRoute}>
           <DataGridDemo />
         </Route>
+        <Route on={complexRoutingDemoRoute}>
+          <ComplexRoutingDemo />
+        </Route>
         <Route on={asyncLookupDemoRoute}>
           <AsyncLookupDemo />
         </Route>
diff --git a/packages/docs/src/demos/ComplexRoutingApp.tsx b/packages/docs/src/demos/ComplexRoutingApp.tsx
new file mode 100644
index 0000000..2ea2ea8
--- /dev/null
+++ b/packages/docs/src/demos/ComplexRoutingApp.tsx
@@ -0,0 +1,174 @@
+import { useMemo } from "react";
+import {
+  DefaultParams,
+  RouteAtom,
+  RouteOptions,
+  routeAtom,
+  rootAtom as defaultRootAtom,
+  staticRouteAtom,
+  validateAtom,
+} from "jarl-atoms";
+import { Link, Route, Switch } from "jarl-react";
+import { isValidCalendarDate } from "./blogPosts";
+import { sampleDates, sampleFiles } from "./complexRoutingSamples";
+
+type DateSegment = { year: number; month: number; day: number };
+
+const DATE_SEGMENT = /^(\d{4})-(\d{2})-(\d{2})$/;
+
+/**
+ * Binds one path segment shaped `yyyy-mm-dd` to its numeric parts: no separate segment per part,
+ * unlike the blog demo's `/:year/:month/:day` chain. `routeAtom` is the right primitive here - the
+ * segment syntax itself, not just the value inside it, is non-standard.
+ * exception: Teaching material on public docs site; docstring clarity warranted for custom atoms.
+ */
+const dateSegmentRouteAtom = <Parent extends DefaultParams>(options?: RouteOptions<Parent>) =>
+  routeAtom<DateSegment, Parent>(
+    (path) => {
+      const match = DATE_SEGMENT.exec(path);
+      if (!match) return undefined;
+      return { year: Number(match[1]), month: Number(match[2]), day: Number(match[3]) };
+    },
+    ({ year, month, day }) =>
+      `${String(year).padStart(4, "0")}-${String(month).padStart(2, "0")}-${String(day).padStart(2, "0")}`,
+    options,
+  );
+
+type FilenameSegment = { name: string; ext: string };
+
+const FILENAME_SEGMENT = /^(.+)\.([^.]+)$/;
+
+/** Binds one path segment shaped `name.ext` to its two parts, e.g. `report.pdf` -> `{ name:
+ * "report", ext: "pdf" }`. A segment with no extension doesn't match. */
+const filenameRouteAtom = <Parent extends DefaultParams>(options?: RouteOptions<Parent>) =>
+  routeAtom<FilenameSegment, Parent>(
+    (path) => {
+      const match = FILENAME_SEGMENT.exec(path);
+      return match ? { name: match[1], ext: match[2] } : undefined;
+    },
+    (values) => `${values.name}.${values.ext}`,
+    options,
+  );
+
+// The demo's whole route tree hangs off whatever root it is given, so the app
+// never knows the URL it is mounted on.
+const createComplexRoutes = (root: RouteAtom<DefaultParams>) => {
+  const archive = staticRouteAtom("archive", { parent: root });
+  const archiveDate = validateAtom(dateSegmentRouteAtom({ parent: archive }), ({ year, month, day }) =>
+    isValidCalendarDate(year, month, day),
+  );
+  const files = staticRouteAtom("files", { parent: root });
+  const file = filenameRouteAtom({ parent: files });
+  return { root, archive, archiveDate, files, file };
+};
+
+type ComplexRoutes = ReturnType<typeof createComplexRoutes>;
+
+const FILE_KIND: Record<string, string> = {
+  pdf: "document",
+  txt: "text file",
+  zip: "archive",
+};
+
+const ComplexNav = ({ routes }: { routes: ComplexRoutes }) => (
+  <nav>
+    <Link route={routes.root} to={{}} exact>
+      Overview
+    </Link>
+  </nav>
+);
+
+const dateFromSegment = (segment: string): DateSegment => {
+  const [year, month, day] = segment.split("-").map(Number);
+  return { year, month, day };
+};
+
+const ComplexIndex = ({ routes }: { routes: ComplexRoutes }) => (
+  <div>
+    <h3>Custom path segments</h3>
+    <p>Dates as one `yyyy-mm-dd` segment, validated against the real calendar:</p>
+    <ul>
+      {sampleDates.map((date) => (
+        <li key={date}>
+          <Link route={routes.archiveDate} to={dateFromSegment(date)}>
+            /archive/{date}
+          </Link>
+        </li>
+      ))}
+    </ul>
+    <p>Filenames as one `name.ext` segment:</p>
+    <ul>
+      {sampleFiles.map(({ name, ext, label }) => (
+        <li key={`${name}.${ext}`}>
+          <Link route={routes.file} to={{ name, ext }}>
+            /files/{name}.{ext}
+          </Link>{" "}
+          &mdash; {label}
+        </li>
+      ))}
+    </ul>
+  </div>
+);
+
+const ComplexNotFound = ({ routes }: { routes: ComplexRoutes }) => (
+  <div>
+    <h3>Not found</h3>
+    <p>
+      No custom segment here matched: an out-of-range date, an invalid calendar date, or a filename with no extension.
+    </p>
+    <p>
+      <Link route={routes.root} to={{}}>
+        Back to overview
+      </Link>
+    </p>
+  </div>
+);
+
+const ArchivePage = ({ year, month, day }: DateSegment) => (
+  <div>
+    <h3>Archive for {`${year}-${String(month).padStart(2, "0")}-${String(day).padStart(2, "0")}`}</h3>
+    <p>
+      Parsed from a single path segment into <code>{`{ year: ${year}, month: ${month}, day: ${day} }`}</code>.
+    </p>
+  </div>
+);
+
+const FilePage = ({ name, ext }: FilenameSegment) => (
+  <div>
+    <h3>
+      {name}.{ext}
+    </h3>
+    <p>
+      Parsed into <code>{`{ name: "${name}", ext: "${ext}" }`}</code> &mdash; treated here as a{" "}
+      {FILE_KIND[ext] ?? "file of unknown type"}.
+    </p>
+  </div>
+);
+
+/**
+ * Self-contained demo of custom single-segment path atoms, built directly on `routeAtom` rather
+ * than `staticRouteAtom`/`paramRouteAtom`: `yyyy-mm-dd` under `/archive`, gated on the real
+ * calendar via `validateAtom`, and `name.ext` under `/files`. Pass the route atom it is mounted
+ * on as `rootAtom` and it builds its own tree under that.
+ */
+export const ComplexRoutingApp = ({ rootAtom = defaultRootAtom }: { rootAtom?: RouteAtom<DefaultParams> }) => {
+  const routes = useMemo(() => createComplexRoutes(rootAtom), [rootAtom]);
+  return (
+    <>
+      <ComplexNav routes={routes} />
+      <Switch fallback={<ComplexNotFound routes={routes} />}>
+        <Route on={routes.root} exact>
+          <ComplexIndex routes={routes} />
+        </Route>
+        <Route on={routes.archiveDate} exact>
+          {(values) => <ArchivePage {...values} />}
+        </Route>
+        <Route on={routes.file} exact>
+          {(values) => <FilePage {...values} />}
+        </Route>
+      </Switch>
+    </>
+  );
+};
+
+export default ComplexRoutingApp;
diff --git a/packages/docs/src/demos/complexRoutingSamples.ts b/packages/docs/src/demos/complexRoutingSamples.ts
new file mode 100644
index 0000000..60b03d9
--- /dev/null
+++ b/packages/docs/src/demos/complexRoutingSamples.ts
@@ -0,0 +1,16 @@
+// 2024 is a leap year, 2023 isn't - both shown in the UI to demonstrate validation, but only the valid one prerendered.
+export const sampleDates = ["2024-02-29", "2023-02-29"];
+
+export const sampleFiles = [
+  { name: "report", ext: "pdf", label: "A PDF report" },
+  { name: "notes", ext: "txt", label: "A plain-text file" },
+  { name: "archive.2024", ext: "zip", label: "A filename with a dot of its own" },
+];
+
+/** Every concrete path this demo's SSG build should prerender. */
+export const complexRoutingStaticPaths = (): string[] => [
+  "/demos/complex-routing",
+  // Only prerender the valid leap-year date; the invalid one demonstrates validateAtom's rejection in the live demo.
+  "/demos/complex-routing/archive/2024-02-29",
+  ...sampleFiles.map(({ name, ext }) => `/demos/complex-routing/files/${name}.${ext}`),
+];
diff --git a/packages/docs/src/pages/ComplexRoutingDemo.tsx b/packages/docs/src/pages/ComplexRoutingDemo.tsx
new file mode 100644
index 0000000..1a62fce
--- /dev/null
+++ b/packages/docs/src/pages/ComplexRoutingDemo.tsx
@@ -0,0 +1,16 @@
+import { complexRoutingDemoRoute } from "../router/routes";
+import { ComplexRoutingApp } from "../demos/ComplexRoutingApp";
+import DemoPage from "../lib/DemoPage";
+import demoSource from "../demos/ComplexRoutingApp.tsx?raw";
+
+export const ComplexRoutingDemo = () => (
+  <DemoPage
+    title="Live demo: complex routing (custom path segments)"
+    sourcePath="packages/docs/src/demos/ComplexRoutingApp.tsx"
+    source={demoSource}
+  >
+    <ComplexRoutingApp rootAtom={complexRoutingDemoRoute} />
+  </DemoPage>
+);
+
+export default ComplexRoutingDemo;
diff --git a/packages/docs/src/pages/DemosIndex.tsx b/packages/docs/src/pages/DemosIndex.tsx
index 9b16b80..7d52440 100644
--- a/packages/docs/src/pages/DemosIndex.tsx
+++ b/packages/docs/src/pages/DemosIndex.tsx
@@ -1,6 +1,12 @@
 import { Link } from "jarl-react";
 import LinkList from "../lib/LinkList";
-import { asyncLookupDemoRoute, basicRoutingDemoRoute, blogRoutingDemoRoute, dataGridDemoRoute } from "../router/routes";
+import {
+  asyncLookupDemoRoute,
+  basicRoutingDemoRoute,
+  blogRoutingDemoRoute,
+  complexRoutingDemoRoute,
+  dataGridDemoRoute,
+} from "../router/routes";
 
 export const DemosIndex = () => (
   <>
@@ -34,6 +40,13 @@ export const DemosIndex = () => (
         &mdash; a table whose filter text and sort column live in <code>queryParamAtom</code>s chained off the mount
         route, so the grid&apos;s state is shareable and moves with back/forward navigation.
       </li>
+      <li>
+        <Link route={complexRoutingDemoRoute} to={{}}>
+          Complex routing
+        </Link>{" "}
+        &mdash; custom single-segment path atoms built on <code>routeAtom</code> directly: <code>yyyy-mm-dd</code> gated
+        on the real calendar with <code>validateAtom</code>, and <code>name.ext</code> filenames.
+      </li>
       <li>
         <Link route={asyncLookupDemoRoute} to={{}}>
           Async lookup
diff --git a/packages/docs/src/router/routes.ts b/packages/docs/src/router/routes.ts
index ff232c7..8b0c945 100644
--- a/packages/docs/src/router/routes.ts
+++ b/packages/docs/src/router/routes.ts
@@ -8,6 +8,7 @@
 import { atom } from "jotai";
 import { asyncRouteAtom, notAtom, rootAtom, staticRouteAtom, paramRouteAtom } from "jarl-atoms";
 import { blogStaticPaths } from "../demos/blogPosts";
+import { complexRoutingStaticPaths } from "../demos/complexRoutingSamples";
 import { articleSlugs, findArticle } from "../demos/asyncArticles";
 import { changelogStaticPaths } from "../pages/changelogEntries";
 
@@ -39,6 +40,11 @@ export const blogRoutingDemoRoute = staticRouteAtom("blog-routing", { parent: de
 // chained inside DataGridApp, on its own basePath-scoped root.
 export const dataGridDemoRoute = staticRouteAtom("data-grid", { parent: demosIndexRoute });
 
+// Complex routing demo: the site's own mount point. The demo's own /archive/:date and
+// /files/:file trees, built on custom single-segment path atoms, live inside
+// ComplexRoutingApp, on its own basePath-scoped root.
+export const complexRoutingDemoRoute = staticRouteAtom("complex-routing", { parent: demosIndexRoute });
+
 // Async-lookup demo: /demos/async-lookup/:slug exists only if the demo's fake database has an
 // article at that slug, and the article it found rides along on the route's own values. Its
 // nested atoms stay module-level, unlike the blog demo's, because the server render needs them:
@@ -63,19 +69,25 @@ const exactRouteMissedAtom = notAtom(
   basicRoutingDemoPageRoute,
   blogRoutingDemoRoute,
   dataGridDemoRoute,
+  complexRoutingDemoRoute,
   asyncLookupDemoRoute,
   asyncArticleRoute,
 );
 
 /**
  * Whether the current location has nothing behind it, which is what makes a server render's
- * *status code* right and not just its HTML. Everything under the changelog's and the blog demo's
- * mounts counts as found - both route their own subtree and render their own not-found views. The
- * async demo gets no such blanket, and lists `asyncArticleRoute` rather than `asyncLookupSlugRoute`:
- * an unknown slug is a genuine miss, even though the demo page still renders its own not-found view.
+ * *status code* right and not just its HTML. Everything under the changelog's, the blog demo's
+ * and the complex-routing demo's mounts counts as found - all three route their own subtree and
+ * render their own not-found views. The async demo gets no such blanket, and lists
+ * `asyncArticleRoute` rather than `asyncLookupSlugRoute`: an unknown slug is a genuine miss, even
+ * though the demo page still renders its own not-found view.
  */
 export const notFoundAtom = atom(
-  (get) => get(exactRouteMissedAtom) && !get(changelogRoute).match && !get(blogRoutingDemoRoute).match,
+  (get) =>
+    get(exactRouteMissedAtom) &&
+    !get(changelogRoute).match &&
+    !get(blogRoutingDemoRoute).match &&
+    !get(complexRoutingDemoRoute).match,
 );
 
 export type DocName = "getting-started" | "data-loading" | "path-variables";
@@ -107,6 +119,7 @@ export const staticPaths: string[] = [
   "/demos/basic-routing/about",
   ...blogStaticPaths(),
   "/demos/data-grid",
+  ...complexRoutingStaticPaths(),
   "/demos/async-lookup",
   ...articleSlugs().map((slug) => `/demos/async-lookup/${slug}`),
 ];