diff --git a/CHANGELOG.md b/CHANGELOG.md
index df289d500..25fef7462 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,27 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- The full OpenGraph / Twitter card set the Sphinx lecture sites emit, on every
+  page: `og:type`, `og:site_name`, `og:url` (from a new `site_url` option; myst's `site.domains` never reaches the theme), a site-level
+  `og:image` / `twitter:image` when the page has no thumbnail (new
+  `og_logo_url` / `twitter_logo_url` options, named as in the book theme),
+  `twitter:site`, and `og:locale` from `current_language`. `twitter:site` had
+  never rendered: upstream puts it in the root route's meta, which the article
+  route's replaces under Remix v2 semantics. Phase 6 of the book-theme parity
+  plan ([#92](https://github.com/QuantEcon/quantecon-theme.mystmd/issues/92)) ([#197](https://github.com/QuantEcon/quantecon-theme.mystmd/pull/197)).
+- Collapsible stderr: a notebook cell's stderr stream is folded behind a
+  "⚠ Code warnings" disclosure, closed by default, as the Sphinx build's
+  `stderr-warnings.js` does. A native `<details>` around the stream at render
+  time rather than DOM surgery after load, so it holds in server-rendered HTML
+  without a script; stdout in the same cell stays visible
+  ([#92](https://github.com/QuantEcon/quantecon-theme.mystmd/issues/92)) ([#197](https://github.com/QuantEcon/quantecon-theme.mystmd/pull/197)).
+- A `docs/` feature reference mirroring the book theme's `docs/user/*` pages
+  (configuration, layout, authors, launch, notebooks, git metadata, code
+  highlighting, text colour schemes, dark mode, RTL and editions,
+  announcements), each naming its `myst.yml` keys and what has no counterpart
+  ([#92](https://github.com/QuantEcon/quantecon-theme.mystmd/issues/92)) ([#197](https://github.com/QuantEcon/quantecon-theme.mystmd/pull/197)).
+
 ### Fixed
 - The "On this page" panel is pinned, tracks scrolling and lists subsections,
   as the Sphinx sites' `sticky_contents` panel does. It scrolled off with the
diff --git a/PLAN.md b/PLAN.md
index b2ccd0797..517314fe1 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -484,16 +484,20 @@ for the same translated sites).
 
 **Goal:** close the smaller gaps and verify assumptions.
 
-- [ ] **OpenGraph/Twitter parity:** the book-theme emits a full OG + Twitter card set;
+- [x] **OpenGraph/Twitter parity:** the book-theme emits a full OG + Twitter card set;
       `root.tsx` currently uses `getMetaTagsForSite` (title/description/twitter). Add
       `og:image`/`twitter:image` (logo), `og:type`, `og:site_name`, etc., driven from
-      site config.
-- [ ] **Collapsible stderr warnings:** confirm whether `@myst-theme/jupyter` already
+      site config. *Done (#92): `app/seo.ts` adds `og:type`, `og:site_name`, `og:url`
+      (from a `site_url` option), site-level images (`og_logo_url` / `twitter_logo_url`),
+      `twitter:site` and `og:locale` on top of upstream's article tags.*
+- [x] **Collapsible stderr warnings:** confirm whether `@myst-theme/jupyter` already
       renders notebook stderr in a collapsible/styled way (it may — verify before
-      porting). If not, add an output transform/renderer.
-- [ ] **Docs:** add a `docs/`-style feature reference for the MyST theme mirroring the
+      porting). If not, add an output transform/renderer. *Verified (#92): upstream
+      renders stderr as a plain `<pre class="jupyter-error">`; ported as a native
+      `<details>` around the stderr `output` node (`STDERR_RENDERERS`).*
+- [x] **Docs:** add a `docs/`-style feature reference for the MyST theme mirroring the
       book-theme's `docs/user/*` set, so downstream lecture maintainers have parity
-      documentation.
+      documentation. *Done (#92): `docs/` with one page per book-theme user page.*
 
 **Effort:** S–M. **Risk:** low. **Deps:** none.
 
diff --git a/README.md b/README.md
index 8a0ef1375..45ab53863 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,8 @@ QuantEcon lectures and books, distributed as a zip attached to each
 - Notebook launch (Google Colab) with configurable repo, branch and paths
 - In-page live compute via Thebe (JupyterLite / Pyodide by default)
 - Git history in page headers ("Last changed" plus an inline changelog)
+- Full OpenGraph / Twitter card meta tags, and collapsible stderr on notebook cells
+- A `docs/` feature reference mirroring the book theme's user guide
 - Page Footer based on MyST Content
 - Bundled QuantEcon brand assets
 
@@ -205,6 +207,24 @@ One trap: a page whose `site:` frontmatter sets any of these keys has its whole
 `site:` block replaced by the validated keys, so an undeclared `site.git_metadata`
 on the same page is lost. Keep the two on different pages.
 
+### Meta tags
+
+Every page carries the OpenGraph and Twitter card set the Sphinx lecture sites
+emit: `og:title`, `og:description`, `og:type` (`website`), `og:site_name`,
+`og:url`, `og:image`, `og:locale`, and `twitter:card`, `twitter:site`,
+`twitter:creator`, `twitter:title`, `twitter:description`, `twitter:image`.
+Four `site.options` keys feed them: `site_url` (the public URL, for
+`og:url`; myst's `site.domains` does not reach the theme), `twitter`, and
+the two image URLs `og_logo_url` / `twitter_logo_url`, named as in the book
+theme so a lecture repo copies its values across. A page's own thumbnail takes precedence for
+`og:image`.
+
+### Collapsible stderr
+
+A notebook cell's stderr stream is folded behind a "⚠ Code warnings"
+disclosure, closed by default, as on the Sphinx sites; stdout in the same cell
+stays visible. It is a native `<details>`, so it works without JavaScript.
+
 ## Site options
 
 Everything the theme reads from `site.options` is declared in
@@ -218,6 +238,8 @@ block inside a string (`key: |`), which the theme parses.
 | Option | Scope | Purpose |
 | ------ | ----- | ------- |
 | `twitter` | site | Handle for the `twitter:site` / `twitter:creator` card meta tags |
+| `site_url` | site | The site's public URL, for `og:url` ([Meta tags](#meta-tags)) |
+| `og_logo_url`, `twitter_logo_url` | site | Site-level images for `og:image` / `twitter:image` when a page has no thumbnail ([Meta tags](#meta-tags)) |
 | `favicon` | site | Favicon file, relative to `myst.yml`; served at `/favicon.ico` (the QuantEcon lectures favicon when unset) |
 | `analytics_google`, `analytics_plausible` | site | Analytics IDs, rendered by `@myst-theme/site` |
 | `hide_toc`, `hide_search` | site or page | Hide the contents drawer / the search control |
diff --git a/app/renderers.tsx b/app/renderers.tsx
index def6ee2f3..dd9cca95b 100644
--- a/app/renderers.tsx
+++ b/app/renderers.tsx
@@ -1,6 +1,7 @@
 import type { GenericNode } from 'myst-common';
 import type { NodeRenderers } from '@myst-theme/providers';
 import { MyST } from 'myst-to-react';
+import { OUTPUT_RENDERERS } from '@myst-theme/jupyter';
 
 /**
  * Fancy ordered lists (QuantEcon/mystmd#50): `list` nodes carry `style`
@@ -65,3 +66,38 @@ export const LIST_RENDERERS: NodeRenderers = {
     );
   },
 };
+
+/**
+ * Collapsible stderr (Phase 6, #92). The Sphinx build's `stderr-warnings.js`
+ * folds a cell's stderr streams behind a "Code warnings" button after page
+ * load; upstream @myst-theme/jupyter renders them as a plain `<pre
+ * class="jupyter-error">`. Same fold, done at render: a stderr stream
+ * `output` node is wrapped in a native `<details>`, closed by default, so it
+ * works in the server-rendered HTML with no script and no DOM surgery. Every
+ * other output goes to upstream's renderer untouched. Styled by the
+ * `.qe-stderr` block in styles/quantecon.css.
+ */
+const UpstreamOutput = OUTPUT_RENDERERS.output as (props: {
+  node: GenericNode;
+  className?: string;
+}) => JSX.Element | null;
+
+export const STDERR_RENDERERS: NodeRenderers = {
+  output(props: { node: GenericNode; className?: string }) {
+    const data = props.node.jupyter_data as { output_type?: string; name?: string } | undefined;
+    if (data?.output_type === 'stream' && data?.name === 'stderr') {
+      return (
+        <details className="qe-stderr">
+          <summary>
+            <span className="qe-stderr__icon" aria-hidden="true">
+              ⚠
+            </span>{' '}
+            Code warnings
+          </summary>
+          <UpstreamOutput {...props} />
+        </details>
+      );
+    }
+    return <UpstreamOutput {...props} />;
+  },
+};
diff --git a/app/root.tsx b/app/root.tsx
index 054365c08..ed770c13f 100644
--- a/app/root.tsx
+++ b/app/root.tsx
@@ -20,7 +20,7 @@ import type { ISearch, MystSearchIndex } from '@myst-theme/search';
 import { SEARCH_ATTRIBUTES_ORDERED } from '@myst-theme/search';
 import { useCallback } from 'react';
 import { JUPYTER_RENDERERS } from '@myst-theme/jupyter';
-import { LIST_RENDERERS } from './renderers';
+import { LIST_RENDERERS, STDERR_RENDERERS } from './renderers';
 import { Document } from './components/Document';
 import { htmlDir, htmlLang } from './i18n';
 import type { TemplateOptions } from './types';
@@ -33,6 +33,8 @@ const RENDERERS: NodeRenderers = mergeRenderers([
   defaultRenderers,
   JUPYTER_RENDERERS,
   LIST_RENDERERS,
+  // After JUPYTER_RENDERERS: wraps upstream's `output` renderer (#92).
+  STDERR_RENDERERS,
 ]);
 
 export const meta: V2_MetaFunction<typeof loader> = ({ data }) => {
diff --git a/app/routes/$.tsx b/app/routes/$.tsx
index ca1e80b45..27f884d85 100644
--- a/app/routes/$.tsx
+++ b/app/routes/$.tsx
@@ -13,6 +13,7 @@ import type { SiteManifest } from 'myst-config';
 import { ErrorPage } from '~/components/ErrorPage';
 import { Page } from '~/components/Page';
 import { hreflangLinks } from '~/i18n';
+import { mergeMeta, socialMetaTags } from '~/seo';
 
 // Never re-run the loader on a navigation that changes neither pathname nor
 // search (Back off an in-page anchor on a static build) -- #186.
@@ -37,8 +38,17 @@ export const meta: V2_MetaFunction<typeof loader> = ({ data, matches, location }
   );
   const baseurl = rootMatch?.data?.BASE_URL;
 
+  // Phase 6 (#92): the Sphinx sites' full OpenGraph / Twitter set on top of
+  // upstream's article tags -- see app/seo.ts for what upstream leaves out.
+  const social = socialMetaTags({
+    domains: config?.domains,
+    siteTitle: config?.title ?? project?.title,
+    pageImage: (page?.thumbnailOptimized || page?.thumbnail) ?? (project?.thumbnailOptimized || project?.thumbnail) ?? undefined,
+    pathname: `${baseurl ?? ''}${location.pathname}`,
+    options: config?.options as any,
+  });
   return [
-    ...getMetaTagsForArticle({
+    ...mergeMeta(getMetaTagsForArticle({
       origin: '',
       url: location.pathname,
       title: page?.title ? `${page.title}${siteTitle ? ` - ${siteTitle}` : ''}` : siteTitle,
@@ -49,7 +59,7 @@ export const meta: V2_MetaFunction<typeof loader> = ({ data, matches, location }
         undefined,
       twitter: config?.options?.twitter,
       keywords: page?.keywords ?? project?.keywords ?? config?.keywords ?? [],
-    }),
+    }), social),
     // hreflang alternates for the translated editions (Phase 4, #90).
     ...hreflangLinks(config?.options, location.pathname, baseurl),
   ];
diff --git a/app/routes/_index.tsx b/app/routes/_index.tsx
index 431252552..eb302778c 100644
--- a/app/routes/_index.tsx
+++ b/app/routes/_index.tsx
@@ -9,6 +9,7 @@ import { getProject } from '@myst-theme/common';
 
 import { Page } from '~/components/Page';
 import { hreflangLinks } from '~/i18n';
+import { mergeMeta, socialMetaTags } from '~/seo';
 
 // Never re-run the loader on a navigation that changes neither pathname nor
 // search (Back off an in-page anchor on a static build) -- #186.
@@ -27,8 +28,17 @@ export const meta: V2_MetaFunction<typeof loader> = ({ data, matches, location }
   );
   const baseurl = rootMatch?.data?.BASE_URL;
 
+  // Phase 6 (#92): the Sphinx sites' full OpenGraph / Twitter set on top of
+  // upstream's article tags -- see app/seo.ts for what upstream leaves out.
+  const social = socialMetaTags({
+    domains: config?.domains,
+    siteTitle: config?.title ?? project?.title,
+    pageImage: (project.thumbnailOptimized || project.thumbnail) ?? undefined,
+    pathname: `${baseurl ?? ''}${location.pathname}`,
+    options: config?.options as any,
+  });
   return [
-    ...getMetaTagsForArticle({
+    ...mergeMeta(getMetaTagsForArticle({
       origin: '',
       url: location.pathname,
       title: config?.title ?? project.title,
@@ -36,7 +46,7 @@ export const meta: V2_MetaFunction<typeof loader> = ({ data, matches, location }
       image: (project.thumbnailOptimized || project.thumbnail) ?? undefined,
       keywords: config.keywords ?? project.keywords ?? [],
       twitter: config?.options?.twitter,
-    }),
+    }), social),
     // hreflang alternates for the translated editions (Phase 4, #90).
     ...hreflangLinks(config?.options, location.pathname, baseurl),
   ];
diff --git a/app/seo.ts b/app/seo.ts
new file mode 100644
index 000000000..c1cf5a72a
--- /dev/null
+++ b/app/seo.ts
@@ -0,0 +1,123 @@
+/**
+ * Social / SEO meta tags (Phase 6, #92) -- the full OpenGraph and Twitter
+ * card set the Sphinx lecture sites emit, on top of what @myst-theme/site's
+ * `getMetaTagsForArticle` already produces (title, description, keywords,
+ * og:title/description/url/image, twitter:card/creator/title/description/
+ * image/alt).
+ *
+ * What upstream leaves out, and the Sphinx sites ship on every page:
+ *
+ *   og:type        "website" (Sphinx: every lecture page)
+ *   og:site_name   the site title
+ *   og:url         upstream needs an `origin`, which the routes never had.
+ *                  It comes from the `site_url` option (the Sphinx sites'
+ *                  `html_baseurl`); `site.domains` would be the natural
+ *                  source, but the CLI's site manifest does not carry it, so
+ *                  it is only a fallback should that change
+ *   og:image /     a site-level image when the page has no thumbnail --
+ *   twitter:image  `og_logo_url` and `twitter_logo_url`, the book theme's
+ *                  option names, so a lecture repo copies its values across
+ *   twitter:site   upstream puts it in the root route's meta, which Remix v2
+ *                  replaces with the article route's, so it never rendered
+ *   og:locale      from `current_language` (Phase 4), when set
+ *
+ * Pure TypeScript with no React; tests/unit/seo.test.mjs runs it under
+ * `node --test` with type stripping like the other helpers.
+ */
+import type { V2_MetaDescriptor } from '@remix-run/react';
+
+export interface SeoSiteOptions {
+  site_url?: string;
+  twitter?: string;
+  og_logo_url?: string;
+  twitter_logo_url?: string;
+  current_language?: string;
+}
+
+export interface SeoInput {
+  /** `site.domains` from myst.yml, if the manifest ever carries it; `options.site_url` is the real source. */
+  domains?: string[];
+  /** Site title, for og:site_name. */
+  siteTitle?: string;
+  /** The page's own image, if any (thumbnail); site-level images fill in. */
+  pageImage?: string;
+  /** Path of the page, including the static build's base URL. */
+  pathname: string;
+  options?: SeoSiteOptions;
+}
+
+/**
+ * The canonical origin: `site_url` (an absolute URL, trailing slash and path
+ * dropped to the origin), else `https://<first domain>` -- the CLI validates
+ * domains as bare hosts.
+ */
+export function siteOrigin(siteUrl?: string, domains?: string[]): string | undefined {
+  const fromOption = siteUrl?.trim();
+  if (fromOption) {
+    try {
+      return new URL(/^https?:\/\//i.test(fromOption) ? fromOption : `https://${fromOption}`).origin;
+    } catch {
+      // fall through to domains
+    }
+  }
+  const host = domains?.find((d) => typeof d === 'string' && d.trim());
+  if (!host) return undefined;
+  const h = host.trim().replace(/\/+$/, '');
+  return /^https?:\/\//i.test(h) ? h : `https://${h}`;
+}
+
+function handle(twitter?: string): string | undefined {
+  const t = twitter?.trim().replace(/^@/, '');
+  return t ? `@${t}` : undefined;
+}
+
+/** BCP 47 code to an OpenGraph locale (`en` -> `en_US`, `zh-cn` -> `zh_CN`). */
+export function ogLocale(code?: string): string | undefined {
+  const c = code?.trim();
+  if (!c) return undefined;
+  const [lang, region] = c.split(/[-_]/);
+  if (!lang) return undefined;
+  if (region) return `${lang.toLowerCase()}_${region.toUpperCase()}`;
+  const defaults: Record<string, string> = { en: 'en_US', fa: 'fa_IR', fr: 'fr_FR', zh: 'zh_CN', es: 'es_ES', ja: 'ja_JP' };
+  return defaults[lang.toLowerCase()] ?? lang.toLowerCase();
+}
+
+/**
+ * The tags to add to (or replace in) upstream's article set. Applied by
+ * `mergeMeta`, which drops an upstream tag with the same name/property first,
+ * so a site-level image does not sit beside a missing page image and
+ * twitter:image follows the site's Twitter logo when one is configured.
+ */
+export function socialMetaTags({ domains, siteTitle, pageImage, pathname, options }: SeoInput): V2_MetaDescriptor[] {
+  const origin = siteOrigin(options?.site_url, domains);
+  const image = pageImage || options?.og_logo_url;
+  const twitterImage = options?.twitter_logo_url || image;
+  const tags: V2_MetaDescriptor[] = [{ property: 'og:type', content: 'website' }];
+  if (siteTitle) tags.push({ property: 'og:site_name', content: siteTitle });
+  if (origin) tags.push({ property: 'og:url', content: `${origin}${pathname}` });
+  if (image) tags.push({ property: 'og:image', content: image });
+  const site = handle(options?.twitter);
+  if (site) {
+    tags.push({ name: 'twitter:site', content: site });
+    tags.push({ name: 'twitter:card', content: 'summary' });
+  }
+  if (twitterImage && (site || twitterImage !== pageImage)) {
+    tags.push({ name: 'twitter:image', content: twitterImage });
+  }
+  const locale = ogLocale(options?.current_language);
+  if (locale) tags.push({ property: 'og:locale', content: locale });
+  return tags;
+}
+
+function key(tag: V2_MetaDescriptor): string | undefined {
+  const t = tag as Record<string, unknown>;
+  if (typeof t.property === 'string') return `property:${t.property}`;
+  if (typeof t.name === 'string') return `name:${t.name}`;
+  return undefined;
+}
+
+/** `additions` win over `base` on the same name/property; order otherwise kept. */
+export function mergeMeta(base: V2_MetaDescriptor[], additions: V2_MetaDescriptor[]): V2_MetaDescriptor[] {
+  const replaced = new Set(additions.map(key).filter((k): k is string => !!k));
+  return [...base.filter((t) => !replaced.has(key(t) ?? '')), ...additions];
+}
diff --git a/app/types.ts b/app/types.ts
index e52e5b873..d0226061e 100644
--- a/app/types.ts
+++ b/app/types.ts
@@ -12,6 +12,9 @@ export interface TemplateOptions {
 
   // Meta / SEO and analytics, passed through to @myst-theme/site.
   twitter?: string; // handle for twitter:site / twitter:creator, `@` optional
+  site_url?: string; // public URL, for og:url (#92); site.domains never reaches the manifest
+  og_logo_url?: string; // og:image when the page has no thumbnail (#92)
+  twitter_logo_url?: string; // twitter:image; falls back to og_logo_url (#92)
   favicon?: string; // declared `file`: the CLI copies it and rewrites this to its served path
   analytics_google?: string;
   analytics_plausible?: string;
diff --git a/docs/announcements.md b/docs/announcements.md
new file mode 100644
index 000000000..cfb0ad7f8
--- /dev/null
+++ b/docs/announcements.md
@@ -0,0 +1,7 @@
+# Announcement banner
+
+The Sphinx theme can show a dismissible site-wide banner (`announcement` in
+`html_theme_options`). This theme does not offer one: no deployed lecture site
+configures it, and the parity work covers the book-theme feature set as the
+lecture sites actually use it. If a series needs a banner, open a request on
+the theme repository with the use case; the header is the natural place for it.
diff --git a/docs/authors.md b/docs/authors.md
new file mode 100644
index 000000000..ebdd4645a
--- /dev/null
+++ b/docs/authors.md
@@ -0,0 +1,36 @@
+# Authors and translators
+
+## Authors
+
+Page-level `authors` frontmatter renders as the byline in the page header, as on
+the Sphinx sites:
+
+```yaml
+---
+authors:
+  - name: Thomas J. Sargent
+  - name: John Stachurski
+---
+```
+
+Project-level authors in `myst.yml` apply to every page.
+
+## Translators
+
+A translated edition credits its translators after the byline. Set them
+site-wide under `site.options`, as a YAML block (template options are
+scalar-only), with an optional label in the edition's language:
+
+```yaml
+site:
+  options:
+    translators: |
+      - name: مترجم نمونه
+        url: https://example.org/translator
+    translators_label: ترجمهٔ
+```
+
+A page overrides the list under `site:` in its frontmatter (replace, never
+merge); an empty value there suppresses the credit on that page. The label
+defaults to "Translated by"; an empty string hides it. See
+[rtl-support](rtl-support.md) for the rest of the multilingual configuration.
diff --git a/docs/code-highlighting.md b/docs/code-highlighting.md
new file mode 100644
index 000000000..5e42f0821
--- /dev/null
+++ b/docs/code-highlighting.md
@@ -0,0 +1,14 @@
+# Code highlighting
+
+Code blocks use QuantEcon's own token palette, the Sphinx lecture sites'
+default `qetheme_code_style`, in light and dark mode. MyST tokenises with
+highlight.js rather than Pygments, so the palette is mapped scope by scope onto
+the `hljs-*` classes; the mapping, and the two Pygments classes highlight.js has
+no scope for (operators and module names), are documented in
+`styles/quantecon.css`.
+
+Only the default style ships. No lecture repository sets a different
+`qetheme_code_style`, so the alternative palettes and the Pygments toggle the
+Sphinx theme offers are deferred until a consumer asks. Five of the light-mode
+token colours fall short of WCAG AA on white; whether to darken them is an open
+two-theme decision (theme issue #172), since they are the deployed sites' values.
diff --git a/docs/configuration.md b/docs/configuration.md
new file mode 100644
index 000000000..a3d1222d5
--- /dev/null
+++ b/docs/configuration.md
@@ -0,0 +1,54 @@
+# Configuration
+
+Everything the theme reads from `site.options` is declared in
+[`template.yml`](../template.yml). The MyST CLI validates `site.options` against
+that list and **drops any key the template does not declare**, so the list is
+the contract, not documentation. Template options are scalar-only (boolean,
+string, number, choice, file), so structured values are written as a YAML block
+inside a string (`key: |`), which the theme parses.
+
+No option has a default in `template.yml`, deliberately: a declared default is
+written into every page's validated `site:` block and would override the
+site-wide value. Defaults live in the code that reads each option and are given
+below.
+
+## Options
+
+| Option | Type | Scope | Default | Purpose |
+| --- | --- | --- | --- | --- |
+| `site_url` | string | site | — | the site's public URL, for `og:url` |
+| `twitter` | string | site | — | handle for `twitter:site` / `twitter:creator`; `@` optional |
+| `og_logo_url` | string | site | — | `og:image` when a page has no thumbnail |
+| `twitter_logo_url` | string | site | — | `twitter:image`; falls back to `og_logo_url` |
+| `favicon` | file | site | the QuantEcon lectures favicon | served at `/favicon.ico` |
+| `analytics_google` | string | site | — | Google Analytics measurement ID |
+| `analytics_plausible` | string | site | — | Plausible domain |
+| `hide_toc` | boolean | site or page | `false` | hide the contents drawer and its toggle |
+| `hide_search` | boolean | site or page | `false` | hide the search control |
+| `launch_repo_url` | string | site | derived | explicit notebook repository |
+| `launch_repo_suffix` | string | site | `.notebooks` | suffix locating the notebook repo |
+| `launch_branch` | string | site | `main` | notebook repo branch |
+| `launch_notebooks_path` | string | site | — | sub-directory of the notebook repo |
+| `launch_source_path` | string | site | — | prefix stripped from the page path |
+| `current_language` | string | site | — | BCP 47 code of this edition |
+| `enable_rtl` | boolean | site | `false` | right-to-left layout |
+| `languages` | YAML block | site | — | the editions, for the language switcher and `hreflang` |
+| `language_switcher_label` | string | site | "Switch language" | the switcher's accessible name |
+| `translators` | YAML block | site or page | — | translator credit |
+| `translators_label` | string | site or page | "Translated by" | label before the credit |
+| `git_metadata` | YAML block | page | — | pins the "Last changed" control by hand |
+
+## Page-level values
+
+A per-page value goes under `site:` in the page's frontmatter (for a notebook,
+under `"site"` in the notebook metadata) and is validated against the same
+list. Only the keys marked "site or page" or "page" are read per page.
+
+## Other `site` keys the theme uses
+
+| Key | Purpose |
+| --- | --- |
+| `site.title` | the site name in the header and `og:site_name` |
+| `site.parts.footer` | the footer content ([layout](layout.md)) |
+| `project.github` | commit and edit links, and the notebook repo derivation |
+| `project.thebe` | in-page live compute ([notebooks](notebooks.md)) |
diff --git a/docs/dark-mode.md b/docs/dark-mode.md
new file mode 100644
index 000000000..f72c44d06
--- /dev/null
+++ b/docs/dark-mode.md
@@ -0,0 +1,8 @@
+# Dark mode
+
+The header's theme toggle switches between light and dark, honouring the
+system preference until the reader chooses. The dark theme uses the Sphinx
+sites' dark ground (`#222`) and white text, with dark values for every colour
+token: links white, the code palette's dark variant, the `seoul256` dark
+colours, `#6cb6ff` for the active "On this page" entry and the amber stderr
+fold. The choice persists in the browser.
diff --git a/docs/features/stderr-warnings.md b/docs/features/stderr-warnings.md
new file mode 100644
index 000000000..74f8e6852
--- /dev/null
+++ b/docs/features/stderr-warnings.md
@@ -0,0 +1,21 @@
+# Collapsible stderr warnings
+
+When a notebook cell produces stderr output (typically warnings), the theme
+folds it behind a compact "⚠ Code warnings" control, closed by default, so the
+reader sees the cell's result without the noise and can open the warnings when
+troubleshooting. The Sphinx theme does the same with a script after page load;
+here it is a native `<details>` around the stderr stream, done at render, so it
+holds in the server-rendered HTML with no JavaScript and survives re-renders.
+
+- Applies per stderr stream; stdout and results in the same cell stay visible.
+- Keyboard and screen-reader accessible through the native disclosure.
+- Dark mode supported.
+
+## Customisation
+
+Target these classes:
+
+- `.qe-stderr` — the disclosure
+- `.qe-stderr > summary` — the control
+- `.qe-stderr__icon` — the warning icon
+- `.qe-stderr pre.jupyter-error` — the stream itself
diff --git a/docs/git-metadata.md b/docs/git-metadata.md
new file mode 100644
index 000000000..40509f99b
--- /dev/null
+++ b/docs/git-metadata.md
@@ -0,0 +1,31 @@
+# Git history in page headers
+
+The page header shows "Last changed: ⟨date⟩", expanding to an inline changelog
+of the most recent commits touching the page, with commit links and a link to
+the file's full history, as the Sphinx sites do. It opens in place above the
+header's blue rule and renders nothing when no data is present.
+
+The data is injected at build time by the git-metadata plugin, a MyST transform
+that runs `git log --follow` per source file and attaches
+`{ last_modified, changelog: [{hash, short_hash, author, date, message}] }` to
+the page. Load it by URL pinned to the theme release the site builds with:
+
+```yaml
+project:
+  github: https://github.com/QuantEcon/lecture-python.myst
+  plugins:
+    - https://raw.githubusercontent.com/QuantEcon/quantecon-theme.mystmd/vX.Y.Z/plugins/git-metadata.mjs
+```
+
+The plugin is moving to the shared `QuantEcon/quantecon-plugins.mystmd`
+repository; the pinned URL form stays supported until that release exists.
+
+Notes:
+
+- Shallow CI clones (`fetch-depth: 1`) yield truncated history; build with
+  `fetch-depth: 0`.
+- `QE_GIT_METADATA_MAX` caps entries per page (default 6); the panel grows to
+  fit rather than scrolling.
+- A page can pin the control by hand with the same shape under `site:` in its
+  frontmatter as a YAML block string (`git_metadata: |`), which takes precedence
+  over the injected data.
diff --git a/docs/index.md b/docs/index.md
new file mode 100644
index 000000000..6758c223e
--- /dev/null
+++ b/docs/index.md
@@ -0,0 +1,45 @@
+# QuantEcon MyST theme — user guide
+
+The feature reference for the QuantEcon lecture theme for MyST / Jupyter Book 2,
+organised the way the Sphinx `quantecon-book-theme` documents its own features so
+a lecture maintainer moving between the two finds the same headings. Each page
+names the `myst.yml` keys involved; the [README](../README.md) has the narrative
+version and the [CHANGELOG](../CHANGELOG.md) the history.
+
+## Quick start
+
+Point `site.template` at a pinned release asset:
+
+```yaml
+# myst.yml
+site:
+  template: https://github.com/QuantEcon/quantecon-theme.mystmd/releases/download/vX.Y.Z/quantecon-theme.zip
+```
+
+Then `myst start` for a live server or `myst build --html` for a static site.
+Every theme option lives under `site.options` and is listed in
+[configuration](configuration.md).
+
+## Pages
+
+| Page | Covers |
+| --- | --- |
+| [configuration](configuration.md) | every `site.options` key, its scope and its default |
+| [layout](layout.md) | header, contents drawer, "On this page" panel, back-to-top, footer |
+| [authors](authors.md) | author line and translator credit |
+| [launch](launch.md) | notebook launch buttons (Colab) and the notebook repo conventions |
+| [notebooks](notebooks.md) | notebook output rendering, live compute, collapsible stderr |
+| [git-metadata](git-metadata.md) | "Last changed" and the inline changelog |
+| [code-highlighting](code-highlighting.md) | the code token palette |
+| [text-color-schemes](text-color-schemes.md) | emphasis, strong and definition colours |
+| [dark-mode](dark-mode.md) | the dark theme and its tokens |
+| [rtl-support](rtl-support.md) | translated editions, the language switcher, right-to-left layout |
+| [announcements](announcements.md) | site-wide banner (not offered; see the page) |
+| [features/stderr-warnings](features/stderr-warnings.md) | the stderr fold in detail |
+
+## How this relates to the Sphinx theme
+
+The theme reproduces the deployed lecture sites' behaviour as those sites configure
+the Sphinx theme, not every Sphinx option. Where a Sphinx option has no
+counterpart, its page says so and why. The parity work is tracked in the
+repository's `PLAN.md`.
diff --git a/docs/launch.md b/docs/launch.md
new file mode 100644
index 000000000..31745c8a0
--- /dev/null
+++ b/docs/launch.md
@@ -0,0 +1,23 @@
+# Launch buttons
+
+The header's launch control opens the page's notebook in **Google Colab**, the
+single launch target the deployed lecture sites offer. BinderHub and a private
+JupyterHub are deliberately not offered (theme issues #26 and #87). Running
+cells in place is a separate feature; see [notebooks](notebooks.md).
+
+The notebook is looked up in a companion repository, by convention
+`<project.github>.notebooks` on branch `main`, with the page path used as-is.
+Five `site.options` keys adjust that, mirroring the book theme's
+`launch_buttons` settings; all are optional and the defaults reproduce the
+convention:
+
+| Option | Default | Purpose |
+| --- | --- | --- |
+| `launch_repo_suffix` | `.notebooks` | suffix appended to the source repo to locate the notebook repo |
+| `launch_branch` | `main` | branch in the notebook repo |
+| `launch_repo_url` | derived | explicit notebook repository (full URL or `org/repo`) |
+| `launch_notebooks_path` | — | sub-directory of the notebook repo holding the notebooks |
+| `launch_source_path` | — | prefix stripped from the page path (e.g. `lectures/`) |
+
+A `.myst` suffix on the source repository is dropped when deriving the notebook
+repository, so `lecture-python.myst` launches from `lecture-python.notebooks`.
diff --git a/docs/layout.md b/docs/layout.md
new file mode 100644
index 000000000..00d18fd8b
--- /dev/null
+++ b/docs/layout.md
@@ -0,0 +1,53 @@
+# Layout
+
+The page chrome, matched to the deployed Sphinx lecture sites.
+
+## Header
+
+A fixed 50px toolbar: the QuantEcon logo and site title, the contents-drawer
+toggle, and on the right the search trigger, launch button, downloads, dark-mode
+toggle, full-screen toggle and, when configured, the language switcher and the
+live-compute control. Below it, the page header carries the title, the author
+line, the translator credit and the "Last changed" control, above a QuantEcon
+blue rule.
+
+## Contents drawer
+
+The site table of contents is an off-canvas drawer, toggled from the header. It
+is built on the native Popover API, so it opens without JavaScript and closes
+when the search dialog opens. `hide_toc: true` (site-wide or on a page) removes
+it and its toggle.
+
+## "On this page"
+
+The right-hand outline is pinned (`position: fixed` in the margin column),
+lists h2 and h3 headings with their section numbers when numbering is on, and
+marks the section being read in QuantEcon blue, bold, with an inset rule
+(`aria-current="location"`). The rule is the Sphinx scrollspy's: a section is
+current once its heading has passed 120px from the top, and the last section is
+current at the bottom of the page. Past the viewport height the panel scrolls
+internally behind a fade. Subsections collapse to the current branch as the
+Sphinx panel does under `contents_autoexpand`: only the sections show until
+you scroll into one, its subsections then expand, and the parent of a current
+subsection is expanded but not marked.
+
+## Back to top
+
+A "↑ Top" link in the margin column, visible after 80px of scrolling, as a plain
+`#top` fragment link.
+
+## Footer
+
+`site.parts.footer` names a Markdown file rendered as the site footer, matching
+the Sphinx sites' footer block:
+
+```yaml
+site:
+  parts:
+    footer: footer.md
+```
+
+## Widths
+
+An 800px body column with a 200px margin column on each side at 1280px and up;
+below `lg` (1024px) the outline column is hidden and the layout is single-column.
diff --git a/docs/notebooks.md b/docs/notebooks.md
new file mode 100644
index 000000000..489eb321e
--- /dev/null
+++ b/docs/notebooks.md
@@ -0,0 +1,36 @@
+# Notebooks
+
+## Output rendering
+
+Notebook outputs render through `@myst-theme/jupyter`: streams and errors as
+`<pre>`, execute results and display data by MIME type (text, HTML, images,
+Plotly and widgets). Long outputs are clipped with a scroll region.
+
+## Collapsible stderr
+
+A cell's stderr stream is folded behind a "⚠ Code warnings" disclosure, closed
+by default, so verbose warnings do not break the reading flow; stdout in the
+same cell stays visible. It is a native `<details>`, so it works in the
+server-rendered HTML without a script. Details in
+[features/stderr-warnings](features/stderr-warnings.md).
+
+## Live compute
+
+Cells can run in place through Thebe, opt-in per project under the standard
+`project.thebe` key; the QuantEcon default is JupyterLite, so Python runs in the
+browser via Pyodide with nothing to host:
+
+```yaml
+project:
+  thebe:
+    lite: true
+```
+
+A Power control then appears in the header on notebook pages; connecting swaps
+it for Run / Restart / Clear. Pyodide runs pure Python and the packages built
+for it (numpy, scipy, pandas, matplotlib, sympy); numba and JAX do not import.
+`binder:` and `server:` backends are available through the same key for
+projects that need a full environment.
+
+The deployed Sphinx lecture sites set `thebe: false`, so a series moving from
+them changes nothing by leaving `project.thebe` unset.
diff --git a/docs/rtl-support.md b/docs/rtl-support.md
new file mode 100644
index 000000000..2194dde77
--- /dev/null
+++ b/docs/rtl-support.md
@@ -0,0 +1,37 @@
+# Translated editions and right-to-left support
+
+## Editions and the language switcher
+
+An edition declares its language and its siblings under `site.options`; with
+two or more entries the header shows a language switcher linking to the same
+page in each edition, and every page carries `hreflang` alternates (the first
+entry is `x-default`):
+
+```yaml
+site:
+  options:
+    current_language: fa
+    language_switcher_label: تغییر زبان
+    languages: |
+      - code: en
+        name: English
+        url: https://python-programming.quantecon.org
+      - code: fa
+        name: فارسی
+        url: https://quantecon.github.io/lecture-python-programming.fa
+```
+
+`languages` is a YAML block in a string because template options are
+scalar-only. `current_language` also sets the document `lang`, marks the active
+switcher entry and drives `og:locale`.
+
+## Right-to-left
+
+`enable_rtl: true` renders the document `dir="rtl"`. The layout uses logical
+properties throughout, so the header, the contents drawer, the outline, list
+markers (including parenthesised fancy markers) and the translator credit
+mirror. A Persian fixture in the repository's visual tests keeps it that way.
+
+## Translator credit
+
+See [authors](authors.md).
diff --git a/docs/text-color-schemes.md b/docs/text-color-schemes.md
new file mode 100644
index 000000000..c98be6d34
--- /dev/null
+++ b/docs/text-color-schemes.md
@@ -0,0 +1,18 @@
+# Text colour schemes
+
+Emphasis, strong text and definition terms render in the Sphinx sites' default
+`seoul256` scheme: teal `em`, amber `strong` and `dt`, both upright at weight
+550, alongside the existing inline-literal colour. They are custom properties
+with dark-mode values:
+
+| Property | Light | Dark |
+| --- | --- | --- |
+| `--qe-emphasis-color` | `#005f5f` | `#5fafaf` |
+| `--qe-strong-color` | `#875f00` | `#d7af5f` |
+| `--qe-definition-color` | strong | strong |
+| `--qe-literal-color` | `#af5f5f` | `#d78787` |
+| `--qe-link-color` | `#0072bc` | `#fff` |
+
+Only the default scheme ships: no lecture repository sets `color_scheme`, so the
+`gruvbox` and `none` switches and the custom-CSS hook are deferred until a
+consumer asks for one.
diff --git a/styles/quantecon.css b/styles/quantecon.css
index b206dec26..2391a4b69 100644
--- a/styles/quantecon.css
+++ b/styles/quantecon.css
@@ -601,6 +601,56 @@
     border-inline-start-color: #6cb6ff;
   }
 
+  /* Collapsible stderr (#92): the Sphinx build's amber "Code warnings"
+     fold (_stderr.scss), as a native <details>. Colours are the book
+     theme's: #ffc107 border and icon, #856404 label (7.0:1 on white). */
+  .qe-stderr {
+    margin: 0.5rem 0;
+    border: 1px solid #ffc107;
+    border-radius: 4px;
+    overflow: hidden;
+  }
+  .qe-stderr > summary {
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+    padding: 0.5rem 1rem;
+    cursor: pointer;
+    font-size: 0.9rem;
+    font-weight: 600;
+    color: #856404;
+    list-style: none;
+  }
+  .qe-stderr > summary::-webkit-details-marker {
+    display: none;
+  }
+  .qe-stderr > summary::after {
+    content: "\25B6"; /* the chevron, rotated when open */
+    margin-inline-start: auto;
+    font-size: 0.7rem;
+    transition: transform 0.2s ease;
+  }
+  .qe-stderr[open] > summary::after {
+    transform: rotate(90deg);
+  }
+  .qe-stderr > summary:hover {
+    background-color: #fff9e6;
+  }
+  .qe-stderr > summary:focus-visible {
+    outline: 2px solid #ffc107;
+    outline-offset: -2px;
+  }
+  .qe-stderr__icon {
+    color: #ffc107;
+    font-size: 1.1rem;
+  }
+  .dark .qe-stderr > summary {
+    color: #ffd54f;
+  }
+  .dark .qe-stderr > summary:hover {
+    background-color: rgba(255, 193, 7, 0.08);
+  }
+
   .qe-back-to-top a {
     /* `rem` for the same reason as the footer: pinned to the Sphinx button's
        size, not the content base. The awkward figure is exactly .85rem of the
diff --git a/template.yml b/template.yml
index e543e4a2d..693773989 100644
--- a/template.yml
+++ b/template.yml
@@ -68,6 +68,22 @@ options:
     description: >
       Twitter/X handle for the `twitter:site` and `twitter:creator` card meta
       tags, with or without the leading `@`.
+  - id: site_url
+    type: string
+    description: >
+      The site's public URL (the Sphinx sites' `html_baseurl`), for the
+      absolute `og:url` on every page. `site.domains` would be the natural
+      source but does not reach the theme.
+  - id: og_logo_url
+    type: string
+    description: >
+      Absolute URL of the image for `og:image` when a page has no thumbnail
+      (the book theme's `og_logo_url`).
+  - id: twitter_logo_url
+    type: string
+    description: >
+      Absolute URL of the image for `twitter:image` (the book theme's
+      `twitter_logo_url`); falls back to the OpenGraph image.
   - id: favicon
     type: file
     description: >
diff --git a/tests/unit/seo.test.mjs b/tests/unit/seo.test.mjs
new file mode 100644
index 000000000..2c2c2d315
--- /dev/null
+++ b/tests/unit/seo.test.mjs
@@ -0,0 +1,95 @@
+/**
+ * Unit tests for the social/SEO meta helpers (app/seo.ts, #92). Run with
+ * `npm run test:unit` (node --test with type stripping, Node >= 23.6).
+ */
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+
+import { mergeMeta, ogLocale, siteOrigin, socialMetaTags } from '../../app/seo.ts';
+
+const byKey = (tags) => Object.fromEntries(tags.map((t) => [t.property ?? t.name, t.content]));
+
+test('siteOrigin: site_url wins and is reduced to an origin; domains are the fallback', () => {
+  assert.equal(siteOrigin('https://python-programming.quantecon.org/'), 'https://python-programming.quantecon.org');
+  assert.equal(siteOrigin('https://quantecon.github.io/lecture-python-programming.fa/'), 'https://quantecon.github.io');
+  assert.equal(siteOrigin('example.org'), 'https://example.org');
+  assert.equal(siteOrigin(undefined, ['python-programming.quantecon.org']), 'https://python-programming.quantecon.org');
+  assert.equal(siteOrigin('', ['', ' example.org/ ']), 'https://example.org');
+  assert.equal(siteOrigin(undefined, ['http://localhost:3000']), 'http://localhost:3000');
+  assert.equal(siteOrigin(undefined, undefined), undefined);
+  assert.equal(siteOrigin('   ', []), undefined);
+});
+
+test('ogLocale: BCP 47 to OpenGraph', () => {
+  assert.equal(ogLocale('en'), 'en_US');
+  assert.equal(ogLocale('zh-cn'), 'zh_CN');
+  assert.equal(ogLocale('fa'), 'fa_IR');
+  assert.equal(ogLocale('pt-BR'), 'pt_BR');
+  assert.equal(ogLocale('xx'), 'xx');
+  assert.equal(ogLocale(undefined), undefined);
+});
+
+test('the Sphinx set, on a lecture page with the site-level images', () => {
+  const tags = byKey(
+    socialMetaTags({
+      siteTitle: 'Python Programming for Economics and Finance',
+      pathname: '/python-by-example/',
+      options: {
+        site_url: 'https://python-programming.quantecon.org',
+        twitter: 'quantecon',
+        og_logo_url: 'https://assets.quantecon.org/img/qe-og-logo.png',
+        twitter_logo_url: 'https://assets.quantecon.org/img/qe-twitter-logo.png',
+        current_language: 'en',
+      },
+    }),
+  );
+  assert.deepEqual(tags, {
+    'og:type': 'website',
+    'og:site_name': 'Python Programming for Economics and Finance',
+    'og:url': 'https://python-programming.quantecon.org/python-by-example/',
+    'og:image': 'https://assets.quantecon.org/img/qe-og-logo.png',
+    'twitter:site': '@quantecon',
+    'twitter:card': 'summary',
+    'twitter:image': 'https://assets.quantecon.org/img/qe-twitter-logo.png',
+    'og:locale': 'en_US',
+  });
+});
+
+test('a page thumbnail beats the site image for og:image; twitter:image follows the Twitter logo', () => {
+  const tags = byKey(
+    socialMetaTags({
+      pathname: '/p',
+      pageImage: '/thumb.png',
+      options: { og_logo_url: 'https://x/og.png', twitter_logo_url: 'https://x/tw.png', twitter: '@qe' },
+    }),
+  );
+  assert.equal(tags['og:image'], '/thumb.png');
+  assert.equal(tags['twitter:image'], 'https://x/tw.png');
+  assert.equal(tags['twitter:site'], '@qe');
+});
+
+test('nothing configured: only og:type, and no dangling twitter tags', () => {
+  const tags = socialMetaTags({ pathname: '/p' });
+  assert.deepEqual(tags, [{ property: 'og:type', content: 'website' }]);
+});
+
+test('mergeMeta replaces same-key upstream tags and keeps the rest in order', () => {
+  const base = [
+    { title: 'T' },
+    { property: 'og:title', content: 'T' },
+    { name: 'twitter:card', content: 'summary_large_image' },
+    { property: 'og:image', content: '/old.png' },
+  ];
+  const merged = mergeMeta(base, [
+    { property: 'og:image', content: '/new.png' },
+    { name: 'twitter:card', content: 'summary' },
+    { property: 'og:type', content: 'website' },
+  ]);
+  assert.deepEqual(merged, [
+    { title: 'T' },
+    { property: 'og:title', content: 'T' },
+    { property: 'og:image', content: '/new.png' },
+    { name: 'twitter:card', content: 'summary' },
+    { property: 'og:type', content: 'website' },
+  ]);
+});
diff --git a/tests/visual/fixture-no-thebe/myst.yml.in b/tests/visual/fixture-no-thebe/myst.yml.in
index d48c9b7e3..65461bb81 100644
--- a/tests/visual/fixture-no-thebe/myst.yml.in
+++ b/tests/visual/fixture-no-thebe/myst.yml.in
@@ -22,3 +22,10 @@ site:
   title: QE Theme No-Thebe Fixture
   template: __THEME__
   options:
+    # Social meta (#92), asserted in theme.spec.ts ("social-meta"). `site_url`
+    # feeds og:url; myst's own `site.domains` never reaches the theme's manifest.
+    site_url: https://example.org
+    twitter: quantecon
+    og_logo_url: https://assets.example.org/qe-og-logo.png
+    twitter_logo_url: https://assets.example.org/qe-twitter-logo.png
+    current_language: en
diff --git a/tests/visual/fixture-no-thebe/notebook.ipynb b/tests/visual/fixture-no-thebe/notebook.ipynb
index cd2ffd450..2bc895283 100644
--- a/tests/visual/fixture-no-thebe/notebook.ipynb
+++ b/tests/visual/fixture-no-thebe/notebook.ipynb
@@ -68,6 +68,33 @@
    "source": [
     "raise ValueError(\"a deliberate error to render the traceback\")"
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stderr",
+     "output_type": "stream",
+     "text": [
+      "W0910 10:15:26.780179 cuda_executor.cc:1802] GPU interconnect information not available\n",
+      "UserWarning: a deliberate warning on stderr, folded behind 'Code warnings' (#92)\n"
+     ]
+    },
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "and a normal line on stdout, left visible\n"
+     ]
+    }
+   ],
+   "source": [
+    "import warnings\n",
+    "warnings.warn('a deliberate warning on stderr')\n",
+    "print('and a normal line on stdout, left visible')"
+   ]
   }
  ],
  "metadata": {
@@ -83,4 +110,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 5
-}
+}
\ No newline at end of file
diff --git a/tests/visual/theme.spec.ts b/tests/visual/theme.spec.ts
index b1efa8eee..0c545c5f2 100644
--- a/tests/visual/theme.spec.ts
+++ b/tests/visual/theme.spec.ts
@@ -430,6 +430,55 @@ test.describe("On this page outline (#182)", () => {
   });
 });
 
+test.describe("Meta/SEO and notebook output polish (#92)", () => {
+  const noThebeBase = `http://localhost:${process.env.NO_THEBE_PORT || "3112"}`;
+  const meta = (page: Page, sel: string) => page.locator(`head meta[${sel}]`);
+
+  // The Sphinx lecture sites' OpenGraph / Twitter set, on a lecture page. The
+  // no-thebe fixture declares `site_url`, `twitter`, both logo URLs and
+  // `current_language`; nothing here depends on the page having a thumbnail.
+  test("social-meta", async ({ page }, testInfo) => {
+    test.skip(testInfo.project.name !== "desktop-chrome", "not viewport-dependent");
+    await page.goto(`${noThebeBase}/notebook`, { waitUntil: "domcontentloaded" });
+    const expectTag = async (sel: string, content: string | RegExp) =>
+      expect(meta(page, sel)).toHaveAttribute("content", content);
+    await expectTag('property="og:type"', "website");
+    await expectTag('property="og:site_name"', "QE Theme No-Thebe Fixture");
+    await expectTag('property="og:url"', "https://example.org/notebook");
+    await expectTag('property="og:image"', "https://assets.example.org/qe-og-logo.png");
+    await expectTag('property="og:locale"', "en_US");
+    await expectTag('name="twitter:site"', "@quantecon");
+    await expectTag('name="twitter:creator"', "@quantecon");
+    await expectTag('name="twitter:card"', "summary");
+    await expectTag('name="twitter:image"', "https://assets.example.org/qe-twitter-logo.png");
+    // Replaced, not duplicated: one og:image, one twitter:card.
+    await expect(meta(page, 'property="og:image"')).toHaveCount(1);
+    await expect(meta(page, 'name="twitter:card"')).toHaveCount(1);
+  });
+
+  // A cell's stderr stream is folded behind a "Code warnings" disclosure,
+  // closed by default, as the Sphinx build's stderr-warnings.js does; stdout
+  // in the same cell stays visible. A native <details>, so it holds in the
+  // server-rendered HTML too.
+  test("stderr-collapsed", async ({ page }, testInfo) => {
+    test.skip(testInfo.project.name !== "desktop-chrome", "not viewport-dependent");
+    await page.goto(`${noThebeBase}/notebook`, { waitUntil: "domcontentloaded" });
+    await settle(page);
+    const fold = page.locator("details.qe-stderr");
+    await expect(fold).toHaveCount(1);
+    await expect(fold).not.toHaveAttribute("open", "");
+    await expect(fold.locator("summary")).toContainText("Code warnings");
+    await expect(fold.locator("pre.jupyter-error")).toBeHidden();
+    // The output, not the source cell that also carries the string.
+    await expect(
+      page.locator("pre.jupyter-output", { hasText: "and a normal line on stdout, left visible" })
+    ).toBeVisible();
+    await fold.locator("summary").click();
+    await expect(fold.locator("pre.jupyter-error")).toBeVisible();
+    await expect(fold.locator("pre.jupyter-error")).toContainText("a deliberate warning on stderr");
+  });
+});
+
 test.describe("Site options reach the theme (#173)", () => {
   // The CLI validates `site.options` against template.yml and DROPS every key
   // the template does not declare, so a theme that reads an undeclared option