diff --git a/README.md b/README.md
index 4750c6a..4e5c150 100644
--- a/README.md
+++ b/README.md
@@ -117,7 +117,7 @@ A diagram renderer, which draws flowcharts and diagrams from a plain-text descri
 
 ### Essentials / Advanced toggle
 
-A two-option switch, provided by the [mkdocs-audience-toggle](#mkdocs-audience-toggle) plugin (configured under `plugins:` in `mkdocs.yml`), that lets a reader hide everything beyond a first-pass beginner curriculum. Content is opted into hiding by marking it `data-fcm-hide="essentials"`:
+A two-option switch, provided by the [mkdocs-audience-toggle](#mkdocs-audience-toggle) plugin (configured under `plugins:` in `mkdocs.yml`), that lets a reader hide everything beyond a first-pass beginner curriculum. Content is opted into hiding by marking it `data-audience-hide="essentials"`:
 
 - On a `##`/`###` heading inside a content page (e.g. functions.md's `## Decorators`), it hides that heading plus every sibling up to the next heading of the same or higher level, and removes the matching entry from the `toc.integrate` sidebar — so there's no dead nav link to something that's hidden.
 - On a homepage card-grid row, it hides just that row. A whole homepage card hides too, once its first paragraph (the only one attr_list can attach the marker to) carries the marker — extra.css has a small `:has()` rule that extends that into hiding the entire `<li>`, since the plugin itself only hides the exact element marked.
@@ -177,10 +177,10 @@ plugins:
 ```
 
 ```markdown
-## Decorators {: data-fcm-hide="essentials" }
+## Decorators {: data-audience-hide="essentials" }
 ```
 
-Material has no built-in way to tailor a page to different readers. The plugin hides a marked heading together with its whole section and its table of contents entry. It switches to the nearest mode that shows the content when a link points to something hidden. It also collapses to icons or moves to its own row on narrow screens. It includes its own Playwright and axe-core tests. See the [plugin's README](https://github.com/luka-sherman/mkdocs-audience-toggle) for all options. This site's setup is under `audience_toggle` in `mkdocs.yml`, with color overrides in `extra.css`'s `#fcm-toggle` rule.
+Material has no built-in way to tailor a page to different readers. The plugin hides a marked heading together with its whole section and its table of contents entry. It switches to the nearest mode that shows the content when a link points to something hidden. It also collapses to icons or moves to its own row on narrow screens. It includes its own Playwright and axe-core tests. See the [plugin's README](https://github.com/luka-sherman/mkdocs-audience-toggle) for all options. This site's setup is under `audience_toggle` in `mkdocs.yml`, with color overrides in `extra.css`'s `#audience-toggle` rule.
 
 ### [mkdocs-cheatsheet](https://pypi.org/project/mkdocs-cheatsheet/)
 
@@ -205,6 +205,21 @@ plugins:
 
 A section with its own cheatsheet page, like Libraries here, shows up on the homepage as title-and-description cards only. The optional header button replaces the logo with a "Cheatsheet" link home. It includes its own Playwright and axe-core tests. See the [plugin's README](https://github.com/luka-sherman/mkdocs-cheatsheet) for all options. This site's setup is under `cheatsheet` in `mkdocs.yml`, with the flag rules in STRUCTURE.md's "Cheatsheet flags" section.
 
+### [mkdocs-light-dark-toggle](https://pypi.org/project/mkdocs-light-dark-toggle/)
+
+An always-visible two-button light/dark switch, replacing Material's native single-knob palette toggle (whose knob is the only clickable spot, and whose current scheme is the only thing you can see). It started as this site's own light/dark JavaScript, and I rewrote it as a published plugin.
+
+```bash
+pip install mkdocs-light-dark-toggle
+```
+
+```yaml
+plugins:
+  - light_dark_toggle
+```
+
+Needs zero configuration to work: it ships with built-in sun/moon icons, unlike `mkdocs-audience-toggle` above where mode icons have no universal meaning and must always be supplied. The native palette radios stay in the DOM, hidden — their own JavaScript still applies and persists the scheme via `localStorage`, the plugin only drives them. It includes its own Playwright and axe-core tests. See the [plugin's README](https://github.com/luka-sherman/mkdocs-light-dark-toggle) for all options. This site's setup is under `light_dark_toggle` in `mkdocs.yml`, with color overrides in `extra.css`'s `#light-dark-toggle` rule.
+
 ## Theme
 
 ### Custom CSS
@@ -327,3 +342,23 @@ The domain is set up via the [docs/CNAME](docs/CNAME) file, which MkDocs copies
 ## License
 
 The content and code in this repo are not licensed for reuse — see [LICENSE](LICENSE).
+
+## AI usage
+
+I used [Claude Code](https://claude.com/claude-code) for:
+
+- Restructuring and rewriting existing content
+- Scaffolding first drafts of library pages based off the site's existing [structure](STRUCTURE.md)
+- Implementing new features (e.g. the [Essentials/Advanced toggle](#essentials--advanced-toggle))
+- Propagating a content or naming change everywhere it's referenced (headings, anchors, homepage keyword links)
+- Diagnosing and fixing test failures (structure, accessibility) instead of just rerunning them
+- Verifying a change with `mkdocs build` and `pytest` before calling it done
+
+How I managed it:
+
+- Scoped to low-judgment, high-volume work — architecture and correctness stayed manual
+- Rewrote drafts in my own words rather than publishing them as-is, so I kept my own mental model of the content I'm teaching from
+- Checked output against [STRUCTURE.md](STRUCTURE.md)
+- Increased [test coverage](#testing) and [continuous integration](#continuous-integration) to protect its integrity
+- Scoped prompts to one task at a time to keep context down
+- After one prompt "fixed" content in bulk on its own, I switched to: report gaps, don't auto-fix content on your behalf
diff --git a/STRUCTURE.md b/STRUCTURE.md
index 1344f3b..6c6f84c 100644
--- a/STRUCTURE.md
+++ b/STRUCTURE.md
@@ -169,16 +169,16 @@ shows library pages as title-and-description cards only, and their links appear
 - **Card text.** Each page's front matter sets `cheatsheet_description` (falling back to
   `description`), plus `cheatsheet_title`, `cheatsheet_icon` or `cheatsheet_title_suffix` (the
   built-in/third-party badge on library cards) where the defaults don't fit.
-- **Essentials mode.** A flagged heading that carries `data-fcm-hide="essentials"` passes it to
+- **Essentials mode.** A flagged heading that carries `data-audience-hide="essentials"` passes it to
   its cheatsheet line or link, so the audience toggle hides both together. A whole card is
-  hidden with `cheatsheet_attrs: {data-fcm-hide: essentials}` in front matter.
+  hidden with `cheatsheet_attrs: {data-audience-hide: essentials}` in front matter.
 - **Verify with a real build.** A renamed heading moves its flag with it, so the cheatsheet can't
   go stale, but `mkdocs build` still prints a `WARNING` for any broken link elsewhere.
 - **Marking content "advanced" for the Essentials/Advanced toggle** — the header's segmented
   control is provided by the `mkdocs-audience-toggle` plugin (configured under `plugins:` in
-  `mkdocs.yml`) and hides content marked `data-fcm-hide="essentials"`. On a content page, append
-  `{ data-fcm-hide="essentials" }` to the heading line (e.g. `functions.md`'s
-  `## Decorators { data-fcm-hide="essentials" }`). This hides that heading, everything up to the
+  `mkdocs.yml`) and hides content marked `data-audience-hide="essentials"`. On a content page, append
+  `{ data-audience-hide="essentials" }` to the heading line (e.g. `functions.md`'s
+  `## Decorators { data-audience-hide="essentials" }`). This hides that heading, everything up to the
   next heading of the same or higher level, and its sidebar entry. The cheatsheet picks the
   marker up from the heading, so there's no second place to tag.
   Which spots to mark, and what counts as advanced/niche vs. core, is a per-editor judgment call
@@ -211,7 +211,7 @@ Pick the existing type that matches the branch, don't invent new ones without a
 | `??? info` | Defining a term/concept adjacent to the page but not the topic itself. |
 | `??? failure` | The negative counterpart to a `success` branch — "this didn't work, here's what to do about it" (e.g. workspace.md's "download Python here" branch when `python --version` doesn't show 3.x.x). |
 | `??? ai` | Opinion/meta content specifically about learning with or around AI (e.g. index.md's FAQ tabs on whether/how to use AI while learning) — not used for teaching content about Python itself. |
-| `??? efficiency` | A runtime/space aside naming the cost behind a choice already shown in prose (e.g. list vs. set membership, `sort()` vs. `sorted()`) — usually a Big O difference, occasionally a constant-factor one (`.get()` vs. two hash lookups, vectorized NumPy vs. a Python loop) where it's still worth flagging but doesn't change the O(...) class. Wrap it in `<div data-fcm-hide="essentials" markdown="block">` on a page that participates in the Essentials/Advanced toggle (skip it on a page that doesn't, like the library reference pages), and close with a link to [style.md's "Efficiency"](docs/practices/style.md#efficiency) section. Formalizes a tradeoff the surrounding prose already states in plain language; doesn't introduce the tradeoff for the first time. |
+| `??? efficiency` | A runtime/space aside naming the cost behind a choice already shown in prose (e.g. list vs. set membership, `sort()` vs. `sorted()`) — usually a Big O difference, occasionally a constant-factor one (`.get()` vs. two hash lookups, vectorized NumPy vs. a Python loop) where it's still worth flagging but doesn't change the O(...) class. Wrap it in `<div data-audience-hide="essentials" markdown="block">` on a page that participates in the Essentials/Advanced toggle (skip it on a page that doesn't, like the library reference pages), and close with a link to [style.md's "Efficiency"](docs/practices/style.md#efficiency) section. Formalizes a tradeoff the surrounding prose already states in plain language; doesn't introduce the tradeoff for the first time. |
 | `!!! example` | An always-open side-by-side comparison the reader is meant to see without a click, not a branch — e.g. "how to loop each type," showing every collection type's loop pattern in one visible table. |
 
 Default to collapsed (`???`), not always-open (`!!!`) — an always-open admonition competes with
diff --git a/docs/javascripts/a11y_patches.js b/docs/javascripts/a11y_patches.js
index 8f6862b..104fbe0 100644
--- a/docs/javascripts/a11y_patches.js
+++ b/docs/javascripts/a11y_patches.js
@@ -11,23 +11,8 @@
     });
   }
 
-  // pymdownx.tasklist (style.md's checklist) renders each `- [ ]` as a real
-  // <input type="checkbox" disabled> wrapped in its own <label>, but that
-  // label contains only the checkbox itself — the item's actual text sits
-  // outside it as a plain sibling — so the checkbox has no accessible name
-  // (axe: "Form elements must have labels"). It's also disabled and never
-  // toggles, so it's not a real control a screen reader user can act on;
-  // hiding it from the accessibility tree lets that text be read on its own
-  // instead of prefixed with a confusing, non-interactive "checkbox" role.
-  function hideDecorativeTaskListCheckboxes() {
-    document.querySelectorAll(".task-list-control > input[type=checkbox]").forEach((el) => {
-      el.setAttribute("aria-hidden", "true");
-    });
-  }
-
   function initA11yPatches() {
     makeScrollRegionsFocusable();
-    hideDecorativeTaskListCheckboxes();
   }
 
   // Material's navigation.instant swaps page content via JS without a full
diff --git a/docs/javascripts/library_spans.js b/docs/javascripts/library_spans.js
new file mode 100644
index 0000000..717064f
--- /dev/null
+++ b/docs/javascripts/library_spans.js
@@ -0,0 +1,43 @@
+(function () {
+  // Recomputes --library-span (the add-on-library boxes' grid span) once the
+  // mkdocs-audience-toggle plugin hides some of their cards in Essentials
+  // mode — the one bit of library-grid behavior no plugin owns, since it's
+  // specific to this site's own card layout.
+
+  // The cheatsheet plugin's --cards-N class sizes each library box for its full card count; hiding cards
+  // in Essentials mode leaves boxes too wide. Recompute the visible count
+  // into --library-span so extra.css can override --cards-N while active.
+  function updateLibrarySpans() {
+    document.querySelectorAll(".library-grid > .md-cheatsheet__group").forEach(function (box) {
+      const cards = box.querySelectorAll(".grid.cards > ul > li");
+      let visible = 0;
+      cards.forEach(function (li) {
+        if (getComputedStyle(li).display !== "none") visible++;
+      });
+      if (visible > 0) box.style.setProperty("--library-span", Math.min(visible, 4));
+    });
+  }
+
+  // The plugin hides content (and sets html[data-audience-mode]) synchronously
+  // from its own script; a MutationObserver callback always fires as a
+  // separate microtask after that synchronous work finishes, so this stays
+  // correctly ordered regardless of which script's DOMContentLoaded/
+  // document$ subscriber happens to run first.
+  function setUp() {
+    if (window.__librarySpanObserverBound) return;
+    window.__librarySpanObserverBound = true;
+    new MutationObserver(updateLibrarySpans).observe(document.documentElement, {
+      attributeFilter: ["data-audience-mode"],
+    });
+    updateLibrarySpans();
+  }
+
+  // navigation.instant swaps page content via JS without a full reload, so
+  // DOMContentLoaded only fires once. document$ is Material's own
+  // observable that emits on every page change, instant or not.
+  if (window.document$) {
+    window.document$.subscribe(setUp);
+  } else {
+    document.addEventListener("DOMContentLoaded", setUp);
+  }
+})();
diff --git a/docs/javascripts/theme_toggle.js b/docs/javascripts/theme_toggle.js
deleted file mode 100644
index b7055f2..0000000
--- a/docs/javascripts/theme_toggle.js
+++ /dev/null
@@ -1,193 +0,0 @@
-(function () {
-  // Light/dark toggle: two always-visible options with a sliding highlight,
-  // next to the palette toggle. Replaces Material's native single-knob
-  // switch, whose knob was the only clickable spot. Native radios stay in
-  // the DOM (hidden); their own JS still applies and persists the scheme,
-  // we just flip `checked` and dispatch change.
-  //
-  // The Essentials/Advanced content toggle used to live in this file too;
-  // it's now the mkdocs-audience-toggle plugin (see mkdocs.yml and
-  // CLAUDE.md's "Planned extraction" section) and no longer touches this
-  // code. This file keeps only the one bit that plugin can't own:
-  // recomputing --library-span (the add-on-library boxes' grid span) once
-  // the plugin hides some of their cards — see updateLibrarySpans below.
-
-  // The cheatsheet plugin's --cards-N class sizes each library box for its full card count; hiding cards
-  // in Essentials mode leaves boxes too wide. Recompute the visible count
-  // into --library-span so extra.css can override --cards-N while active.
-  function updateLibrarySpans() {
-    document.querySelectorAll(".library-grid > .md-cheatsheet__group").forEach(function (box) {
-      const cards = box.querySelectorAll(".grid.cards > ul > li");
-      let visible = 0;
-      cards.forEach(function (li) {
-        if (getComputedStyle(li).display !== "none") visible++;
-      });
-      if (visible > 0) box.style.setProperty("--library-span", Math.min(visible, 4));
-    });
-  }
-
-  // The plugin hides content (and sets html[data-fcm-mode]) synchronously
-  // from its own script; a MutationObserver callback always fires as a
-  // separate microtask after that synchronous work finishes, so this stays
-  // correctly ordered regardless of which script's DOMContentLoaded/
-  // document$ subscriber happens to run first.
-  function setUpLibrarySpanRecompute() {
-    if (window.__librarySpanObserverBound) return;
-    window.__librarySpanObserverBound = true;
-    new MutationObserver(updateLibrarySpans).observe(document.documentElement, {
-      attributeFilter: ["data-fcm-mode"],
-    });
-    updateLibrarySpans();
-  }
-
-  // Disappearing confirmation toast — shows what a click on the light/dark
-  // toggle just changed, since the button itself only shows the current
-  // state, not what changed.
-  //
-  // `iconAttrs` is the dataset to put on the icon span, e.g. {scheme:
-  // "slate"} — matched in extra.css by .pt-mode-icon[data-scheme] to the
-  // same sun/moon icons the toggle itself uses. `body` is optional; pass ""
-  // for a one-line toast (this toggle's own message is self-explanatory).
-  let toastTimer = null;
-  function showToast(label, iconAttrs, body) {
-    let toast = document.getElementById("pt-toast");
-    if (!toast) {
-      toast = document.createElement("div");
-      toast.id = "pt-toast";
-      toast.className = "pt-toast";
-      // status + polite: announced to screen readers without interrupting
-      // whatever they're already reading, same as a visual toast doesn't
-      // steal focus.
-      toast.setAttribute("role", "status");
-      toast.setAttribute("aria-live", "polite");
-      document.body.appendChild(toast);
-    }
-
-    toast.innerHTML = "";
-
-    const title = document.createElement("div");
-    title.className = "pt-toast__title";
-    const icon = document.createElement("span");
-    icon.className = "pt-mode-icon";
-    Object.keys(iconAttrs).forEach(function (key) {
-      icon.dataset[key] = iconAttrs[key];
-    });
-    icon.setAttribute("aria-hidden", "true");
-    title.append(icon, " " + label);
-    toast.append(title);
-
-    if (body) {
-      const bodyEl = document.createElement("div");
-      bodyEl.className = "pt-toast__body";
-      bodyEl.textContent = body;
-      toast.append(bodyEl);
-    }
-
-    // The header's own height isn't fixed across breakpoints (taller with
-    // the tab bar on tablet/desktop) or over time (Material can hide/reveal
-    // it on scroll), so position below it fresh on every call rather than
-    // hardcoding an offset in CSS.
-    const header = document.querySelector(".md-header");
-    const headerBottom = header ? header.getBoundingClientRect().bottom : 0;
-    toast.style.top = Math.max(headerBottom, 0) + 12 + "px";
-
-    // Retrigger the transition even if a toast is already showing (rapid
-    // clicks): drop the class, force layout, then re-add it, instead of
-    // just extending the existing timer.
-    toast.classList.remove("pt-toast--visible");
-    void toast.offsetWidth;
-    toast.classList.add("pt-toast--visible");
-
-    clearTimeout(toastTimer);
-    toastTimer = setTimeout(function () {
-      toast.classList.remove("pt-toast--visible");
-    }, 1400);
-  }
-
-  function getOrCreateThemeToggle() {
-    let container = document.getElementById("pt-theme-toggle");
-    if (container) return container;
-
-    const paletteForm = document.querySelector('[data-md-component="palette"]');
-    if (!paletteForm) return null;
-
-    const lightRadio = paletteForm.querySelector('input[data-md-color-scheme="default"]');
-    const darkRadio = paletteForm.querySelector('input[data-md-color-scheme="slate"]');
-    if (!lightRadio || !darkRadio) return null;
-
-    paletteForm.hidden = true;
-
-    container = document.createElement("div");
-    container.id = "pt-theme-toggle";
-    container.className = "pt-simplify-toggle pt-theme-toggle";
-    container.setAttribute("role", "group");
-    container.setAttribute("aria-label", "Color theme");
-
-    const highlight = document.createElement("span");
-    highlight.className = "pt-simplify-highlight";
-    highlight.setAttribute("aria-hidden", "true");
-
-    const light = document.createElement("button");
-    light.type = "button";
-    light.className = "pt-simplify-option pt-theme-option";
-    light.dataset.scheme = "default";
-    light.title = "Switch to light mode";
-    light.setAttribute("aria-label", "Switch to light mode");
-
-    const dark = document.createElement("button");
-    dark.type = "button";
-    dark.className = "pt-simplify-option pt-theme-option";
-    dark.dataset.scheme = "slate";
-    dark.title = "Switch to dark mode";
-    dark.setAttribute("aria-label", "Switch to dark mode");
-
-    container.append(highlight, dark, light);
-    paletteForm.insertAdjacentElement("beforebegin", container);
-
-    container.addEventListener("click", function (event) {
-      const option = event.target.closest(".pt-theme-option");
-      if (!option) return;
-      const scheme = option.dataset.scheme;
-      const radio = scheme === "slate" ? darkRadio : lightRadio;
-      if (radio.checked) return;
-      radio.checked = true;
-      radio.dispatchEvent(new Event("change", { bubbles: true }));
-      applyThemeState(container);
-      showToast(scheme === "slate" ? "Lights off" : "Lights on", { scheme: scheme }, "");
-    });
-
-    // Sync to whatever scheme Material's own JS actually lands on, not
-    // just what we clicked.
-    lightRadio.addEventListener("change", function () {
-      applyThemeState(container);
-    });
-    darkRadio.addEventListener("change", function () {
-      applyThemeState(container);
-    });
-
-    return container;
-  }
-
-  function applyThemeState(container) {
-    const scheme = document.body.getAttribute("data-md-color-scheme");
-    container.dataset.active = scheme === "slate" ? "dark" : "light";
-    container.querySelectorAll(".pt-theme-option").forEach(function (option) {
-      option.setAttribute("aria-pressed", String(option.dataset.scheme === scheme));
-    });
-  }
-
-  function setUp() {
-    const themeToggle = getOrCreateThemeToggle();
-    if (themeToggle) applyThemeState(themeToggle);
-    setUpLibrarySpanRecompute();
-  }
-
-  // navigation.instant swaps page content via JS without a full reload, so
-  // DOMContentLoaded only fires once. document$ is Material's own
-  // observable that emits on every page change, instant or not.
-  if (window.document$) {
-    window.document$.subscribe(setUp);
-  } else {
-    document.addEventListener("DOMContentLoaded", setUp);
-  }
-})();
diff --git a/docs/libraries/computer_vision/opencv.md b/docs/libraries/computer_vision/opencv.md
index 53c27b4..519d826 100644
--- a/docs/libraries/computer_vision/opencv.md
+++ b/docs/libraries/computer_vision/opencv.md
@@ -3,7 +3,7 @@ cheatsheet_title: OpenCV
 cheatsheet_description: 'Real-time image and video analysis, built directly on NumPy arrays: color spaces, edge detection, face detection.'
 cheatsheet_title_suffix: :material-download-outline:{ .library-badge .library-badge--third-party title="Third-party — install separately with pip" }
 cheatsheet_attrs:
-  data-fcm-hide: essentials
+  data-audience-hide: essentials
 description: >-
   Computer vision in Python with OpenCV: reading and displaying images, color spaces,
   edge detection, contours, and face detection.
diff --git a/docs/libraries/data_analysis/numpy.md b/docs/libraries/data_analysis/numpy.md
index ddc795f..453a998 100644
--- a/docs/libraries/data_analysis/numpy.md
+++ b/docs/libraries/data_analysis/numpy.md
@@ -3,7 +3,7 @@ cheatsheet_title: NumPy
 cheatsheet_description: Fast numeric arrays, with math applied to a whole array at once instead of item by item.
 cheatsheet_title_suffix: :material-download-outline:{ .library-badge .library-badge--third-party title="Third-party — install separately with pip" }
 cheatsheet_attrs:
-  data-fcm-hide: essentials
+  data-audience-hide: essentials
 description: >-
   Fast numeric arrays in Python with NumPy: creating arrays, vectorized math, aggregation,
   and boolean-mask filtering, with runnable examples.
diff --git a/docs/libraries/data_analysis/pandas.md b/docs/libraries/data_analysis/pandas.md
index 0c29ec5..4386f32 100644
--- a/docs/libraries/data_analysis/pandas.md
+++ b/docs/libraries/data_analysis/pandas.md
@@ -3,7 +3,7 @@ cheatsheet_title: pandas
 cheatsheet_description: 'Tabular data: rows and columns, like a spreadsheet, built on top of NumPy.'
 cheatsheet_title_suffix: :material-download-outline:{ .library-badge .library-badge--third-party title="Third-party — install separately with pip" }
 cheatsheet_attrs:
-  data-fcm-hide: essentials
+  data-audience-hide: essentials
 description: >-
   Tabular data in Python with pandas: building a DataFrame, sorting rows, and summarizing
   columns, with runnable examples.
diff --git a/docs/libraries/utilities/collections.md b/docs/libraries/utilities/collections.md
index 610307d..837bb14 100644
--- a/docs/libraries/utilities/collections.md
+++ b/docs/libraries/utilities/collections.md
@@ -3,7 +3,7 @@ cheatsheet_title: collections
 cheatsheet_description: 'Specialized containers: counting items, grouping with defaults, named tuples, fast queues.'
 cheatsheet_title_suffix: :material-language-python:{ .library-badge .library-badge--builtin title="Built-in — included with Python" }
 cheatsheet_attrs:
-  data-fcm-hide: essentials
+  data-audience-hide: essentials
 description: >-
   Specialized container types in Python's collections module: Counter, defaultdict,
   namedtuple, deque, OrderedDict, and ChainMap, with runnable examples.
diff --git a/docs/organization/classes.md b/docs/organization/classes.md
index c8bfc22..419e7ed 100644
--- a/docs/organization/classes.md
+++ b/docs/organization/classes.md
@@ -135,7 +135,7 @@ print(burmese.species)    # "burmese" — a separate copy, not shared
 
 For a value every object should share instead of holding its own copy, see [class attributes](#class-attributes) below.
 
-<div data-fcm-hide="essentials" markdown="block">
+<div data-audience-hide="essentials" markdown="block">
 
 ??? efficiency "For efficiency, use __slots__ when creating many instances"
     | | Time | Space (n instances) |
@@ -321,7 +321,7 @@ print(burmese.kingdom)       # "Animalia" — unaffected
 
 <div class="pfg-section" markdown="block">
 
-## Method decorators { data-fcm-hide="essentials" cs="method decorators" }
+## Method decorators { data-audience-hide="essentials" cs="method decorators" }
 
 Python provides 3 built-in [decorators](functions.md#decorators) for methods that change how the method is called and add functionality:
 
@@ -451,7 +451,7 @@ snake.describe()    # "a 5 ft ball python"        — Snake's own version
 boa.describe()      # "a heavy-bodied constrictor" — Boa's version replaces it
 ```
 
-### Multiple inheritance { data-fcm-hide="essentials" cs="multiple inheritance" }
+### Multiple inheritance { data-audience-hide="essentials" cs="multiple inheritance" }
 
 A class can list more than one parent, comma-separated — it inherits the combined attributes and methods of all of them. When two parents define the same method, Python searches left to right through the parents listed and uses the first match — this search order is called the **MRO** (method resolution order).
 
@@ -570,7 +570,7 @@ print(cobra.warning())    # "handle with extreme caution" — Venomous is listed
 
 <div class="pfg-section" markdown="block">
 
-## Polymorphism { data-fcm-hide="essentials" cs="polymorphism" }
+## Polymorphism { data-audience-hide="essentials" cs="polymorphism" }
 
 **Polymorphism** ("many forms") means the same method or function name behaves differently depending on which object it's called on — so you can call `.describe()` on any snake-like object without needing to know exactly which one it is.
 
@@ -650,7 +650,7 @@ for s in (snake, boa): print(s.describe())
 
 <div class="pfg-section" markdown="block">
 
-## Encapsulation { data-fcm-hide="essentials" cs="encapsulation" }
+## Encapsulation { data-audience-hide="essentials" cs="encapsulation" }
 
 **Encapsulation** restricts direct access to an object's data, so it can only be read or changed through the class's own methods. Python doesn't enforce this the way some other languages do — it's a naming convention the caller is trusted to respect, not a hard restriction.
 
@@ -708,7 +708,7 @@ ball.length_ft = -1    # ValueError — blocked by the setter
 
 <div class="pfg-section" markdown="block">
 
-## Operator overloading { data-fcm-hide="essentials" cs="operator overloading" }
+## Operator overloading { data-audience-hide="essentials" cs="operator overloading" }
 
 Defining a dunder method lets a built-in operator (`==`, `<`, `+`, ...) work on your own objects — the same mechanism as [`__str__()`](#defining-a-class) and [`__repr__()`](#defining-a-class), just for operators instead of printing.
 
@@ -763,7 +763,7 @@ print(ball + burmese)    # 21 — combined length
 
 <div class="pfg-section" markdown="block">
 
-## Dataclasses { data-fcm-hide="essentials" cs="dataclasses" }
+## Dataclasses { data-audience-hide="essentials" cs="dataclasses" }
 
 `@dataclass` generates `__init__()` and `__repr__()` automatically from a list of typed attributes, instead of writing them by hand.
 
@@ -797,7 +797,7 @@ Use it for a class that's mostly just holding data, with little or no custom beh
 
 <div class="pfg-section" markdown="block">
 
-## Abstract base classes { data-fcm-hide="essentials" cs="abstract base classes" }
+## Abstract base classes { data-audience-hide="essentials" cs="abstract base classes" }
 
 An **abstract base class** defines methods that every subclass must implement, using `abc.ABC` and `@abstractmethod`. Trying to create an object from a class that hasn't implemented all of them raises a `TypeError` immediately, instead of failing later when the missing method actually gets called.
 
diff --git a/docs/organization/functions.md b/docs/organization/functions.md
index d9f325a..a649282 100644
--- a/docs/organization/functions.md
+++ b/docs/organization/functions.md
@@ -196,7 +196,7 @@ def describe(**details):
 describe(species="ball", length_ft=5)
 ```
 
-#### Type hints { data-fcm-hide="essentials" cs="type hints" }
+#### Type hints { data-audience-hide="essentials" cs="type hints" }
 
 A type hint on a parameter like `species: str` annotates the type of value it's expected to receive. Python doesn't enforce it, but it can be helpful for you to keep track of it and a separate type checker (like `mypy`) can check for you.
 
@@ -205,7 +205,7 @@ def describe(species: str, length_ft: float):
     return f"a {length_ft} ft {species} python"
 ```
 
-#### Combining categories { data-fcm-hide="essentials" cs="combining argument types" }
+#### Combining categories { data-audience-hide="essentials" cs="combining argument types" }
 
 A single signature can mix kinds of parameters, but must be in this order:
 
@@ -224,7 +224,7 @@ describe("ball", 5, 6, venomous=True, habitat="captive")
 # species = "ball", lengths = (5, 6), venomous = True, details = {"habitat": "captive"}
 ```
 
-#### Positional-only { data-fcm-hide="essentials" cs="positional-only" }
+#### Positional-only { data-audience-hide="essentials" cs="positional-only" }
 
 A `/` in the parameter list marks every parameter before it **positional-only** — it can only be passed by position, never by name. Most parameters don't need this restriction. It mainly shows up in library code, where locking a parameter to positional-only lets the author rename it later without breaking callers who passed it by keyword.
 
@@ -236,7 +236,7 @@ describe("ball", 5)                     # by position — works
 describe(species="ball", length_ft=5)   # TypeError — species is positional-only
 ```
 
-#### Keyword-only { data-fcm-hide="essentials" cs="keyword-only" }
+#### Keyword-only { data-audience-hide="essentials" cs="keyword-only" }
 
 A `*` in the parameter list marks every parameter after it **keyword-only** — it can only be passed by name, never by position. Keyword-only parameters suit options that would be unclear as a bare positional value — `venomous=True` reads clearly at the call site, `True` alone wouldn't.
 
@@ -519,7 +519,7 @@ def show_species():
 
 <div class="pfg-section" markdown="block">
 
-## Recursion { data-fcm-hide="essentials" cs="recursion" }
+## Recursion { data-audience-hide="essentials" cs="recursion" }
 
 A function can call itself — this is called **recursion**, an alternative to a loop for problems that break down into smaller versions of themselves.
 
@@ -561,7 +561,7 @@ Every recursive function needs two parts:
     print("liftoff")
     ```
 
-<div data-fcm-hide="essentials" markdown="block">
+<div data-audience-hide="essentials" markdown="block">
 
 ??? efficiency "For efficiency, use a loop instead of recursion to save memory"
     | | Time | Space |
@@ -601,7 +601,7 @@ Every recursive function needs two parts:
 
 <div class="pfg-section" markdown="block">
 
-## Decorators { data-fcm-hide="essentials" cs="decorators" }
+## Decorators { data-audience-hide="essentials" cs="decorators" }
 
 **`@decorator`** lets you add behavior to a function without editing the function's own code — write the behavior once, then apply it to as many functions as you want. It's written as `@decorator_name`, placed directly above a `def`, and takes one function in, returning a function out[^callable].
 
@@ -785,7 +785,7 @@ print(total_length(5, 12, 8))    # prints "called with (5, 12, 8)", then 25 —
 
 <div class="pfg-section" markdown="block">
 
-## Generators { data-fcm-hide="essentials" cs="generators" }
+## Generators { data-audience-hide="essentials" cs="generators" }
 
 A **generator** is a function that pauses and resumes instead of running start to finish and returning once. Calling it doesn't run the body — it returns a **generator object** that produces values one at a time, only as they're asked for.
 
diff --git a/docs/practices/errors.md b/docs/practices/errors.md
index f5f28ec..a150784 100644
--- a/docs/practices/errors.md
+++ b/docs/practices/errors.md
@@ -381,7 +381,7 @@ finally:
         print(f"found it: {length} ft")   # runs only if try succeeded
     ```
 
-<div data-fcm-hide="essentials" markdown="block">
+<div data-audience-hide="essentials" markdown="block">
 
 ??? efficiency "For efficiency, use try/except when success is the common case"
     | | Time | Space |
diff --git a/docs/practices/style.md b/docs/practices/style.md
index d0d9f9e..403e45a 100644
--- a/docs/practices/style.md
+++ b/docs/practices/style.md
@@ -26,7 +26,7 @@ Code that works isn't automatically code that's easy to read and maintain.
 
 Python runs styled and unstyled code identically, so following PEP 8 doesn't make a script more *correct* — it makes it more *predictable* to read. Anyone who's used Python before recognizes the shape of PEP 8-styled code, so sticking to it means less friction reading someone else's code, and less friction when someone else reads yours.
 
-### File order { data-fcm-hide="essentials" cs="order" }
+### File order { data-audience-hide="essentials" cs="order" }
 
 A Python file conventionally follows the same layout, top to bottom — a linter won't flag this on its own the way it does most of PEP 8, since it's a convention about where things go rather than a formatting rule.[^order-pep8]
 
@@ -79,7 +79,7 @@ length_ft = 4.5        # clear at a glance
 
 A short name is fine when its scope is short too — `for s in species:` is common, since `s` only exists for the one line inside the loop.
 
-### Constants { data-fcm-hide="essentials" cs="constants" }
+### Constants { data-audience-hide="essentials" cs="constants" }
 
 A **constant** is a variable whose value isn't meant to change while the program runs — written in `ALL_CAPS` by convention, so it's easy to tell apart from a regular variable at a glance. Defining one instead of repeating a raw number (a "magic number") gives that number a name explaining what it means.
 
@@ -94,7 +94,7 @@ if length_ft > MAX_TYPICAL_LENGTH_FT:
 
 Constants are usually defined near the top of a file, so they're easy to find and adjust later — see [File Order](#file-order) above.
 
-### Quote style { data-fcm-hide="essentials" cs="quote style" }
+### Quote style { data-audience-hide="essentials" cs="quote style" }
 
 Python treats `'single'` and `"double"` quotes identically for strings — PEP 8 doesn't prefer one over the other, just pick one as your default and stick with it throughout a file, rather than mixing both without reason. (This site uses double quotes.) The one except&zwnj;ion: switch to the other quote character for a string that itself contains a quote, rather than escaping it with a backslash.
 
@@ -148,7 +148,7 @@ species = "ball python"
 length_ft = 4.5
 ```
 
-### Indentation { data-fcm-hide="essentials" cs="indentation" }
+### Indentation { data-audience-hide="essentials" cs="indentation" }
 
 Python uses indentation, not braces, to mark a block — PEP 8's rule is 4 spaces per level, never tabs (mixing the two causes real errors, not just style complaints).
 
@@ -194,7 +194,7 @@ def describe(species, length_ft=4.5):      # PEP 8
     ...
 ```
 
-### Comments { data-fcm-hide="essentials" cs="comments" }
+### Comments { data-audience-hide="essentials" cs="comments" }
 
 An inline comment needs at least two spaces before the `#` and one space after it; a block comment on its own line follows the same one-space-after rule.
 
@@ -263,7 +263,7 @@ def add_sighting(species, log=None):   # Pythonic — a fresh list every call
     return log
 ```
 
-### Truthy checks instead of len(x) > 0 { #truthy-checks data-fcm-hide="essentials" cs="truthy checks" }
+### Truthy checks instead of len(x) > 0 { #truthy-checks data-audience-hide="essentials" cs="truthy checks" }
 
 Test a collection directly — a non-empty list is already truthy.
 
@@ -275,7 +275,7 @@ if species:              # Pythonic — a non-empty list is already truthy
     print("found some")
 ```
 
-### enumerate() instead of range(len(...)) { #enumerate-instead-of-range data-fcm-hide="essentials" cs="enumerate()" }
+### enumerate() instead of range(len(...)) { #enumerate-instead-of-range data-audience-hide="essentials" cs="enumerate()" }
 
 Loop with both the index and the item at once, instead of indexing into the list by hand.
 
@@ -304,7 +304,7 @@ if length_ft is None:                # Pythonic — `is` is the correct tool for
 
 <div class="pfg-section" markdown="block">
 
-## Efficiency { data-fcm-hide="essentials" cs }
+## Efficiency { data-audience-hide="essentials" cs }
 
 Correct code produces the right output.
 
diff --git a/docs/resources/files.md b/docs/resources/files.md
index adf71f0..d9ee4ca 100644
--- a/docs/resources/files.md
+++ b/docs/resources/files.md
@@ -217,7 +217,7 @@ with open("notes.txt", "r") as file:
             print(line.strip())
     ```
 
-<div data-fcm-hide="essentials" markdown="block">
+<div data-audience-hide="essentials" markdown="block">
 
 ??? efficiency "For efficiency, loop over a file instead of reading it all at once"
     | | Time | Space |
@@ -233,7 +233,7 @@ with open("notes.txt", "r") as file:
 
 </div>
 
-#### Seek and tell { data-fcm-hide="essentials" cs="seek(), tell()" }
+#### Seek and tell { data-audience-hide="essentials" cs="seek(), tell()" }
 
 `.tell()` returns the current position in the file, as a character count from the start. `.seek(position)` moves back to a given position, letting you re-read part of a file without closing and reopening it.
 
@@ -344,7 +344,7 @@ with open("notes.txt", "r") as file:
         print(file.read())
     ```
 
-#### "x" create { data-fcm-hide="essentials" cs="create" }
+#### "x" create { data-audience-hide="essentials" cs="create" }
 
 `"x"` is for when overwriting an existing file would be a mistake — it creates the file, but raises `FileExistsError` instead of silently replacing something already there. Like `"w"`, it's write-only — reading from that same file object raises an error, so reading it back means reopening it in `"r"` mode afterward.
 
diff --git a/docs/start/workspace.md b/docs/start/workspace.md
index 3cd47d3..fba3c40 100644
--- a/docs/start/workspace.md
+++ b/docs/start/workspace.md
@@ -148,7 +148,7 @@ That's it! You've written and run your first Python program. From here, you can
 
 <div class="pfg-section" markdown="block">
 
-## Using the terminal { data-fcm-hide="essentials" cs="Terminal, cd, ls, pwd, shortcuts" }
+## Using the terminal { data-audience-hide="essentials" cs="Terminal, cd, ls, pwd, shortcuts" }
 
 The terminal is a text-based way to navigate your computer's files and run programs.
 
@@ -233,7 +233,7 @@ It's good for running Python files that are already finished — either your own
 
 <div class="pfg-section" markdown="block">
 
-## Virtual environments { data-fcm-hide="essentials" cs="virtual environments, activate, pip, requirements.txt, venv" }
+## Virtual environments { data-audience-hide="essentials" cs="virtual environments, activate, pip, requirements.txt, venv" }
 
 Sometimes you'll want to install [external libraries](../libraries/index.md) for your project. A **virtual environment** keeps each project's installed libraries in their own separate folder instead of installing them onto your computer.
 
diff --git a/docs/stylesheets/extra.css b/docs/stylesheets/extra.css
index 6d266dc..e1fc9be 100644
--- a/docs/stylesheets/extra.css
+++ b/docs/stylesheets/extra.css
@@ -587,7 +587,7 @@ input:checked + .md-consent__settings {
   mask-image: var(--md-admonition-icon--python);
 }
 
-/* ---- Custom "efficiency" admonition for runtime/space asides (data-fcm-hide="essentials" only) ---- */
+/* ---- Custom "efficiency" admonition for runtime/space asides (data-audience-hide="essentials" only) ---- */
 
 :root {
   --md-admonition-icon--efficiency: url('data:image/svg+xml;charset=utf-8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M11,15H6L13,1V9H18L11,23V15Z"/></svg>');
@@ -972,271 +972,61 @@ input:checked + .md-consent__settings {
   margin: 0.3rem 0 0.1rem;
 }
 
-/* Light/dark toggle track (docs/javascripts/theme_toggle.js) — both
-   options always visible, sliding highlight behind the active one, next
-   to the palette toggle. Shows on every page.
-
-   The Essentials/Advanced content toggle used to share this same
-   .pt-simplify-* markup/CSS (two named options, one active at a time). It's
-   now the mkdocs-audience-toggle plugin's own #fcm-toggle, styled
-   below via that plugin's --fcm-* variables instead — see "Content mode
-   toggle" further down. */
-.pt-simplify-toggle {
-  position: relative;
-  display: inline-flex;
-  align-items: center;
-  height: 1.2rem;
+/* Light/dark toggle, from the mkdocs-light-dark-toggle plugin configured
+   in mkdocs.yml — see CLAUDE.md's "Planned extraction" section. The
+   plugin's own CSS (light_dark_toggle.css) provides the track/highlight/
+   option/icon layout and built-in sun/moon icons; this site only
+   overrides its --light-dark-* styling hooks to match this site's look,
+   plus the header spacing the plugin doesn't set for itself. */
+#light-dark-toggle {
   margin: 0.4rem 0.2rem;
-  /* currentColor, not a fixed accent — border/highlight/text below track
-     the theme's own ink/bg shades. */
-  border: 0.05rem solid currentColor;
-  border-radius: 1rem;
-  overflow: hidden;
-  /* The site's own background, not transparent — otherwise the inactive
-     option just shows whatever's behind the header (the translucent
-     --md-primary-fg-color, plus the header's own scale/shimmer pattern on
-     top), so the track read inconsistently depending on scroll position
-     and theme. A flat --pt-bg fill keeps the inactive side legible and
-     matches the highlight pill's own solid currentColor fill instead of
-     looking like a hole cut into the header. */
-  background-color: var(--pt-bg);
+  --light-dark-track-bg: var(--pt-bg);
+  --light-dark-active-fg: var(--pt-bg);
 }
 
-.pt-simplify-highlight {
-  position: absolute;
-  top: 0;
-  left: 0;
-  width: 50%;
-  height: 100%;
-  /* Square outer edge gets clipped to the track's own rounding via
-     overflow: hidden above; only the inner (middle) edge needs rounding. */
-  border-radius: 0 1rem 1rem 0;
-  background-color: currentColor;
-  transition: transform 0.2s ease;
-}
-
-.pt-simplify-toggle[data-active="light"] .pt-simplify-highlight {
-  border-radius: 1rem 0 0 1rem;
-  transform: translateX(100%);
-}
-
-.pt-simplify-option {
-  position: relative;
-  z-index: 1;
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  flex: 1;
-  padding: 0 0.5rem;
-  border: none;
-  background: none;
-  color: currentColor;
-  font-family: inherit;
-  font-size: 0.6rem;
-  font-weight: 700;
-  letter-spacing: 0.02em;
-  white-space: nowrap;
-  cursor: pointer;
-}
-
-/* Active option's text sits on the currentColor highlight, so it flips
-   to the bg color for contrast; inactive stays plain currentColor. */
-.pt-simplify-toggle[data-active="light"] .pt-simplify-option[data-scheme="default"],
-.pt-simplify-toggle[data-active="dark"] .pt-simplify-option[data-scheme="slate"] {
-  color: var(--pt-bg);
+/* Matched to #light-dark-toast's look below, via the plugin's own
+   dedicated --light-dark-toast-bg/--light-dark-toast-fg hooks. */
+#light-dark-toast {
+  --light-dark-toast-bg: var(--pt-ink);
+  --light-dark-toast-fg: var(--pt-bg);
+  border-radius: 1.6rem;
+  line-height: 1.4;
+  box-shadow: var(--md-shadow-z2);
+  transition: opacity 0.7s ease, transform 0.7s ease;
 }
 
-/* Reusable sun/moon icon sizing, shared between .pt-theme-option's own
-   ::before (see below) and the toast's real .pt-mode-icon element
-   (docs/javascripts/theme_toggle.js's showToast) — same mask-image
-   technique, so both read as the exact same icon. Sized smaller (0.7rem)
-   than the toast's own override (1.2rem, matching Material's "back to
-   top" icon) since this one sits inside the 1.2rem-tall toggle track
-   itself. */
-.pt-mode-icon {
-  content: "";
-  display: inline-block;
-  width: 0.7rem;
-  height: 0.7rem;
-  flex: none;
-  background-color: currentColor;
-  -webkit-mask-repeat: no-repeat;
-  mask-repeat: no-repeat;
-  -webkit-mask-size: contain;
-  mask-size: contain;
-  -webkit-mask-position: center;
-  mask-position: center;
-}
-
-/* Toast-only override: matches the size of Material's own "back to top"
-   icon (`.md-icon svg`, 1.2rem), per the shared rule's comment above. */
-.pt-mode-icon {
-  width: 1.2rem;
-  height: 1.2rem;
-}
-
-/* Several of Material's own rules (.md-header__option, .md-option:checked
-   + label) beat the plain [hidden] { display: none } UA rule on
-   specificity, so an element we hide via JS (.hidden = true) can silently
-   stay visible — hit this before (the palette form, hidden here via
-   theme_toggle.js). One global override instead of chasing each element
-   type.
-   Excludes Material's own [data-md-component="sidebar"] (the mobile nav
-   drawer, reused as .md-sidebar--primary): Material toggles its `hidden`
-   attribute itself and reveals it via its own more-specific (but
-   non-!important) CSS when the drawer checkbox is checked — our
-   !important here silently beat that and left the hamburger menu
-   permanently empty on mobile, with no console error. Same class of bug
-   as the .md-sidebar--primary gotcha in CLAUDE.md's Navigation section,
-   different cause. */
-[hidden]:not([data-md-component="sidebar"]) {
-  display: none !important;
+#light-dark-toast.light-dark-toast--visible {
+  transition: opacity 0.15s ease, transform 0.15s ease;
 }
 
 /* Content mode toggle (Essentials/Advanced), from the
    mkdocs-audience-toggle plugin configured in mkdocs.yml — see
    CLAUDE.md's "Planned extraction" section. The plugin's own CSS
    (audience_toggle.css) provides the track/highlight/option/icon
-   layout and mobile label-collapse; this site only overrides its --fcm-*
-   styling hooks to match the .pt-simplify-toggle look above, plus the
-   header spacing the plugin doesn't set for itself. */
-#fcm-toggle {
+   layout and mobile label-collapse; this site only overrides its
+   --audience-* styling hooks to match the light/dark toggle's look
+   above, plus the header spacing the plugin doesn't set for itself. */
+#audience-toggle {
   margin: 0.4rem 0.2rem;
-  --fcm-track-bg: var(--pt-bg);
-  --fcm-active-fg: var(--pt-bg);
+  --audience-track-bg: var(--pt-bg);
+  --audience-active-fg: var(--pt-bg);
 }
 
-/* The plugin's own confirmation toast (shown on switching content mode) —
-   matched to .pt-toast's look above (the light/dark toggle's own toast)
-   instead of the plugin's plain default, so both read as the same site
-   chrome element. */
-#fcm-toast {
+/* Matched to #light-dark-toast's look above, via the plugin's own dedicated
+   --audience-toast-bg/--audience-toast-fg hooks (mkdocs-audience-toggle >=0.1.1). */
+#audience-toast {
+  --audience-toast-bg: var(--pt-ink);
+  --audience-toast-fg: var(--pt-bg);
   border-radius: 1.6rem;
-  background-color: var(--md-default-bg-color);
-  color: var(--md-default-fg-color--light);
-  font-weight: 400;
   line-height: 1.4;
   box-shadow: var(--md-shadow-z2);
   transition: opacity 0.7s ease, transform 0.7s ease;
 }
 
-#fcm-toast.fcm-toast--visible {
+#audience-toast.audience-toast--visible {
   transition: opacity 0.15s ease, transform 0.15s ease;
 }
 
-/* Light/dark toggle — shares .pt-simplify-toggle/-highlight/-option, but
-   each option is a fixed choice (sun = light, moon = dark) rather than
-   one element showing whichever mode is current. Native Material markup
-   is hidden but stays in the DOM (its own JS still applies the scheme). */
-.pt-theme-option {
-  padding: 0 0.35rem;
-}
-
-.pt-theme-option::before {
-  content: "";
-  display: block;
-  width: 0.7rem;
-  height: 0.7rem;
-  background-color: currentColor;
-  -webkit-mask-repeat: no-repeat;
-  mask-repeat: no-repeat;
-  -webkit-mask-size: contain;
-  mask-size: contain;
-  -webkit-mask-position: center;
-  mask-position: center;
-}
-
-.pt-theme-option[data-scheme="default"]::before {
-  -webkit-mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 -960 960 960'%3E%3Cpath d='M579-381q41-41 41-99t-41-99q-41-41-99-41t-99 41q-41 41-41 99t41 99q41 41 99 41t99-41Zm-240.5 42.5Q280-397 280-480t58.5-141.5Q397-680 480-680t141.5 58.5Q680-563 680-480t-58.5 141.5Q563-280 480-280t-141.5-58.5ZM200-450H40v-60h160v60Zm720 0H760v-60h160v60ZM450-760v-160h60v160h-60Zm0 720v-160h60v160h-60ZM262-658l-100-97 43-44 96 100-39 41Zm494 496-98-100 41-41 99 98-42 43Zm-99-537 98-99 44 42-99 98-43-41ZM162-205l99-98 42 42-98 99-43-43Zm318-275Z'/%3E%3C/svg%3E");
-  mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 -960 960 960'%3E%3Cpath d='M579-381q41-41 41-99t-41-99q-41-41-99-41t-99 41q-41 41-41 99t41 99q41 41 99 41t99-41Zm-240.5 42.5Q280-397 280-480t58.5-141.5Q397-680 480-680t141.5 58.5Q680-563 680-480t-58.5 141.5Q563-280 480-280t-141.5-58.5ZM200-450H40v-60h160v60Zm720 0H760v-60h160v60ZM450-760v-160h60v160h-60Zm0 720v-160h60v160h-60ZM262-658l-100-97 43-44 96 100-39 41Zm494 496-98-100 41-41 99 98-42 43Zm-99-537 98-99 44 42-99 98-43-41ZM162-205l99-98 42 42-98 99-43-43Zm318-275Z'/%3E%3C/svg%3E");
-}
-
-.pt-theme-option[data-scheme="slate"]::before {
-  -webkit-mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 -960 960 960'%3E%3Cpath d='M480-120q-150 0-255-105T120-480q0-150 105-255t255-105q8 0 17 .5t23 1.5q-36 32-56 79t-20 99q0 90 63 153t153 63q52 0 99-18.5t79-51.5q1 12 1.5 19.5t.5 14.5q0 150-105 255T480-120Zm0-60q109 0 190-67.5T771-406q-25 11-53.67 16.5Q688.67-384 660-384q-114.69 0-195.34-80.66Q384-545.31 384-660q0-24 5-51.5t18-62.5q-98 27-162.5 109.5T180-480q0 125 87.5 212.5T480-180Zm-4-297Z'/%3E%3C/svg%3E");
-  mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 -960 960 960'%3E%3Cpath d='M480-120q-150 0-255-105T120-480q0-150 105-255t255-105q8 0 17 .5t23 1.5q-36 32-56 79t-20 99q0 90 63 153t153 63q52 0 99-18.5t79-51.5q1 12 1.5 19.5t.5 14.5q0 150-105 255T480-120Zm0-60q109 0 190-67.5T771-406q-25 11-53.67 16.5Q688.67-384 660-384q-114.69 0-195.34-80.66Q384-545.31 384-660q0-24 5-51.5t18-62.5q-98 27-162.5 109.5T180-480q0 125 87.5 212.5T480-180Zm-4-297Z'/%3E%3C/svg%3E");
-}
-
-/* Same sun/moon icons, reusable on a real element (not a pseudo-element) —
-   used by the toast (docs/javascripts/theme_toggle.js's showToast)
-   for the light/dark toggle's own "Lights on"/"Lights off" message,
-   keeping it visually consistent with .pt-theme-option's icon. */
-.pt-mode-icon[data-scheme="default"] {
-  -webkit-mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 -960 960 960'%3E%3Cpath d='M579-381q41-41 41-99t-41-99q-41-41-99-41t-99 41q-41 41-41 99t41 99q41 41 99 41t99-41Zm-240.5 42.5Q280-397 280-480t58.5-141.5Q397-680 480-680t141.5 58.5Q680-563 680-480t-58.5 141.5Q563-280 480-280t-141.5-58.5ZM200-450H40v-60h160v60Zm720 0H760v-60h160v60ZM450-760v-160h60v160h-60Zm0 720v-160h60v160h-60ZM262-658l-100-97 43-44 96 100-39 41Zm494 496-98-100 41-41 99 98-42 43Zm-99-537 98-99 44 42-99 98-43-41ZM162-205l99-98 42 42-98 99-43-43Zm318-275Z'/%3E%3C/svg%3E");
-  mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 -960 960 960'%3E%3Cpath d='M579-381q41-41 41-99t-41-99q-41-41-99-41t-99 41q-41 41-41 99t41 99q41 41 99 41t99-41Zm-240.5 42.5Q280-397 280-480t58.5-141.5Q397-680 480-680t141.5 58.5Q680-563 680-480t-58.5 141.5Q563-280 480-280t-141.5-58.5ZM200-450H40v-60h160v60Zm720 0H760v-60h160v60ZM450-760v-160h60v160h-60Zm0 720v-160h60v160h-60ZM262-658l-100-97 43-44 96 100-39 41Zm494 496-98-100 41-41 99 98-42 43Zm-99-537 98-99 44 42-99 98-43-41ZM162-205l99-98 42 42-98 99-43-43Zm318-275Z'/%3E%3C/svg%3E");
-}
-
-.pt-mode-icon[data-scheme="slate"] {
-  -webkit-mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 -960 960 960'%3E%3Cpath d='M480-120q-150 0-255-105T120-480q0-150 105-255t255-105q8 0 17 .5t23 1.5q-36 32-56 79t-20 99q0 90 63 153t153 63q52 0 99-18.5t79-51.5q1 12 1.5 19.5t.5 14.5q0 150-105 255T480-120Zm0-60q109 0 190-67.5T771-406q-25 11-53.67 16.5Q688.67-384 660-384q-114.69 0-195.34-80.66Q384-545.31 384-660q0-24 5-51.5t18-62.5q-98 27-162.5 109.5T180-480q0 125 87.5 212.5T480-180Zm-4-297Z'/%3E%3C/svg%3E");
-  mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 -960 960 960'%3E%3Cpath d='M480-120q-150 0-255-105T120-480q0-150 105-255t255-105q8 0 17 .5t23 1.5q-36 32-56 79t-20 99q0 90 63 153t153 63q52 0 99-18.5t79-51.5q1 12 1.5 19.5t.5 14.5q0 150-105 255T480-120Zm0-60q109 0 190-67.5T771-406q-25 11-53.67 16.5Q688.67-384 660-384q-114.69 0-195.34-80.66Q384-545.31 384-660q0-24 5-51.5t18-62.5q-98 27-162.5 109.5T180-480q0 125 87.5 212.5T480-180Zm-4-297Z'/%3E%3C/svg%3E");
-}
-
-/* Disappearing confirmation toast for the light/dark toggle
-   (docs/javascripts/theme_toggle.js's showToast). Sits just below the header — right where the toggle that triggered it
-   lives — rather than at the bottom of the screen, so it's immediately
-   next to the control the reader just clicked. `top` itself is set inline
-   by showToast() (the header's own height varies: ~48px on mobile, taller
-   on desktop/tablet with the tab bar, and Material can also hide/reveal it
-   on scroll), only the offset-from-header gap lives here. Centered
-   horizontally on both desktop and mobile. Shape/colors match Material's
-   own "back to top" pill (`.md-top`) — same rounded-pill radius, shadow,
-   bg/fg pairing, font size, and padding — so it reads as a native site
-   chrome element rather than a one-off custom popup. */
-.pt-toast {
-  position: fixed;
-  z-index: 1000;
-  left: 50%;
-  transform: translate(-50%, 0);
-  max-width: min(90vw, 22rem);
-  padding: 0.4rem 0.8rem;
-  border-radius: 1.6rem;
-  background-color: var(--md-default-bg-color);
-  color: var(--md-default-fg-color--light);
-  font-size: 0.7rem;
-  line-height: 1.4;
-  text-align: center;
-  box-shadow: var(--md-shadow-z2);
-  opacity: 0;
-  /* none while hidden, so an invisible toast (opacity alone doesn't take
-     it out of hit-testing) doesn't block clicks on whatever's under where
-     it will appear; .pt-toast--visible switches it back to auto so a
-     click on the visible toast is absorbed instead of passing through to
-     the page content behind it. */
-  pointer-events: none;
-  /* Fade only — no slide/transform. The fade-out itself is slow and
-     gentle; showToast() in theme_toggle.js keeps the fully-visible
-     hold time short instead, so the toast still clears the screen quickly
-     overall. */
-  transition: opacity 0.7s ease;
-}
-
-.pt-toast--visible {
-  opacity: 1;
-  pointer-events: auto;
-  /* Fading in can be quick; only the fade-out (the base .pt-toast rule
-     above, used once this class is removed again) is slow. */
-  transition: opacity 0.15s ease;
-}
-
-.pt-toast__title {
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  gap: 0.25rem;
-  font-weight: 700;
-}
-
-/* Only add space below the title when there's actually a body line under
-   it — the light/dark toast's own title is self-explanatory and always
-   passes no body (see showToast() in theme_toggle.js), so this only
-   matters if a future caller adds one. */
-.pt-toast__title:not(:last-child) {
-  margin-bottom: 0.2rem;
-}
-
-.pt-toast__body {
-  font-weight: 400;
-}
-
 .library-grid > .md-cheatsheet__group {
   grid-column: 1 / -1;
 }
@@ -1282,10 +1072,10 @@ input:checked + .md-consent__settings {
   .library-grid > [class*="md-cheatsheet__group--cards-"]:not(.md-cheatsheet__group--cards-1):not(.md-cheatsheet__group--cards-2):not(.md-cheatsheet__group--cards-3) { grid-column: span 4; } /* caps at the grid's own width */
 
   /* --cards-N above is sized for the full card count; Essentials mode
-     hides some, leaving boxes too wide. theme_toggle.js recomputes the
+     hides some, leaving boxes too wide. library_spans.js recomputes the
      visible count into --library-span, overriding --cards-N here (same
      specificity, later in source) while active. */
-  html[data-fcm-mode="essentials"] .library-grid > .md-cheatsheet__group {
+  html[data-audience-mode="essentials"] .library-grid > .md-cheatsheet__group {
     grid-column: span var(--library-span, 4);
   }
 }
diff --git a/docs/types/basics.md b/docs/types/basics.md
index 173cf63..d3b3c57 100644
--- a/docs/types/basics.md
+++ b/docs/types/basics.md
@@ -433,7 +433,7 @@ Strings use the same index and slice syntax as lists. `0` is the first character
     "-".join(["burmese", "python"])  # "burmese-python"
     ```
 
-<div data-fcm-hide="essentials" markdown="block">
+<div data-audience-hide="essentials" markdown="block">
 
 ??? efficiency "For efficiency, use .join() instead of += in a loop"
     | | Time | Space |
diff --git a/docs/types/collections.md b/docs/types/collections.md
index 9641ee3..74225ad 100644
--- a/docs/types/collections.md
+++ b/docs/types/collections.md
@@ -448,7 +448,7 @@ class diagram panel
     See the [collections library page](../libraries/utilities/collections.md) for the rest of `deque`'s
     methods (`rotate()`, `maxlen=`, and more) and for the other list-adjacent tools it adds.
 
-<div data-fcm-hide="essentials" markdown="block">
+<div data-audience-hide="essentials" markdown="block">
 
 ??? efficiency "For efficiency, use append()/pop() instead of insert(0, x)/pop(0)"
     | | Time | Space |
@@ -539,7 +539,7 @@ flowchart LR
     snake.get("weight_lbs", 0)  # 0 — key is missing, so the default is returned instead of None
     ```
 
-<div data-fcm-hide="essentials" markdown="block">
+<div data-audience-hide="essentials" markdown="block">
 
 ??? efficiency "For efficiency, use .get() instead of checking in first"
     | | Time | Space |
@@ -704,7 +704,7 @@ flowchart LR
     snakes["burmese"]["length_ft"]  # 16
     ```
 
-<div data-fcm-hide="essentials" markdown="block">
+<div data-audience-hide="essentials" markdown="block">
 
 ??? efficiency "For efficiency, use a dict instead of a list to look up by key"
     | | Time | Space |
@@ -821,7 +821,7 @@ flowchart LR
 
 <div class="pfg-section" markdown="block">
 
-## Tuples { data-fcm-hide="essentials" cs="tuples, immutable, index" }
+## Tuples { data-audience-hide="essentials" cs="tuples, immutable, index" }
 
 A tuple stores multiple items, in order, written in parentheses. They are **immutable** so the items can't be changed once its created.
 
@@ -1094,7 +1094,7 @@ The **negative index** starts counting down from the end instead, starting at `-
 
 <div class="pfg-section" markdown="block">
 
-## Sets { data-fcm-hide="essentials" cs="sets" }
+## Sets { data-audience-hide="essentials" cs="sets" }
 
 A set stores multiple items, in no particular order, inside a single variable — written with curly braces.
 
@@ -1330,7 +1330,7 @@ These check a relationship between two sets and hand back a `bool`, rather than
     list(set(species))  # ["burmese", "ball", "boa"] — order not guaranteed
     ```
 
-<div data-fcm-hide="essentials" markdown="block">
+<div data-audience-hide="essentials" markdown="block">
 
 ??? efficiency "For efficiency, use a set instead of a list for membership checks"
     | | Time | Space |
diff --git a/mkdocs.yml b/mkdocs.yml
index ca972ea..813e137 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -13,22 +13,33 @@ plugins:
   # here or the site silently loses its search feature.
   - search
   - nested-tabs
-  # Essentials/Advanced content toggle — see extra.css's "Essentials/Advanced
-  # toggle" section for the --fcm-* variable overrides that give it this
-  # site's look, and STRUCTURE.md / CLAUDE.md for the data-fcm-hide="essentials"
-  # marking convention. "Advanced" is listed first and marked default: true
-  # so it keeps showing everything on first visit, matching this site's
-  # prior behavior.
   # Homepage and libraries/index.md card grids, built from {cs} heading
   # flags on each page — see STRUCTURE.md's "Cheatsheet flags" section.
   - cheatsheet:
       button: true
       sort: alphabetical
       group_heading_level: 4
+  # Always-visible light/dark switch, replacing Material's native single-knob
+  # palette toggle — see extra.css's "Light/dark toggle" section for the
+  # --light-dark-* variable overrides that give it this site's look. Listed
+  # before audience_toggle below: it creates #light-dark-toggle, which that
+  # plugin's insert_selector then anchors to — on_config order follows this
+  # plugins: list order, so its script tag (and #light-dark-toggle) must
+  # exist before audience_toggle's own script looks for it.
+  - light_dark_toggle:
+      light:
+        announcement: Lights on
+      dark:
+        announcement: Lights off
+  # Essentials/Advanced content toggle — see extra.css's "Essentials/Advanced
+  # toggle" section for the --audience-* variable overrides that give it this
+  # site's look, and STRUCTURE.md / CLAUDE.md for the data-audience-hide="essentials"
+  # marking convention. "Advanced" is listed first and marked default: true
+  # so it keeps showing everything on first visit, matching this site's
+  # prior behavior.
   - audience_toggle:
       aria_label: Content level
-      # theme_toggle.js creates #pt-theme-toggle before this plugin's script runs.
-      insert_selector: "#pt-theme-toggle"
+      insert_selector: "#light-dark-toggle"
       collapse_labels: true
       query_param: mode
       wrapper_class:
@@ -165,8 +176,6 @@ markdown_extensions:
           format: !!python/name:pymdownx.superfences.fence_code_format
   - pymdownx.tabbed:
       alternate_style: true
-  - pymdownx.tasklist:
-      custom_checkbox: true
   - tables
 
 copyright: '&copy; <span id="copyright-year">2026</span> Luka'
@@ -196,7 +205,7 @@ extra_javascript:
   - javascripts/copyright_year.js
   - javascripts/external_links.js
   - javascripts/homepage_header_title.js
-  - javascripts/theme_toggle.js
+  - javascripts/library_spans.js
   - javascripts/a11y_patches.js
   - https://unpkg.com/mermaid@11/dist/mermaid.min.js
   - javascripts/mermaid_config.js
diff --git a/requirements.txt b/requirements.txt
index 18b02d5..0bed974 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,11 +1,14 @@
 mkdocs
 mkdocs-material
+# Extracted light/dark header toggle — see CLAUDE.md's "Planned extraction"
+# section. Published to PyPI; was a local editable install before 2026-10-01.
+mkdocs-light-dark-toggle==0.1.0
 # Extracted nested-tabs header row — see CLAUDE.md's "Planned extraction"
 # section. Published to PyPI; was a local editable install before 2026-09-23.
 mkdocs-nested-tabs==0.2.0
 # Extracted Essentials/Advanced content toggle — see CLAUDE.md's "Planned
 # extraction" section. Published to PyPI; was a local editable install before 2026-09-26.
-mkdocs-audience-toggle==0.1.0
+mkdocs-audience-toggle==0.1.1
 # Extracted homepage/libraries cheatsheet grid — see CLAUDE.md's "Homepage"
 # section. Published to PyPI 2026-09-27.
 mkdocs-cheatsheet==0.1.0
diff --git a/tests/test_accessibility_browser.py b/tests/test_accessibility_browser.py
index 3740aeb..7218cc3 100644
--- a/tests/test_accessibility_browser.py
+++ b/tests/test_accessibility_browser.py
@@ -37,10 +37,10 @@
 def _select_scheme(page, scheme):
     """Flip Material's palette to `scheme` ('default' = light, 'slate' = dark).
 
-    docs/javascripts/theme_toggle.js replaces the visible light/dark control with its
+    The mkdocs-light-dark-toggle plugin replaces the visible light/dark control with its
     own buttons and hides Material's native radio entirely, so Playwright can't click it
     as a normal user control. Clicking it directly still fires the same input change that
-    Material's own JS (and our buttons) rely on to apply and persist the scheme.
+    Material's own JS (and the plugin's buttons) rely on to apply and persist the scheme.
     """
     page.evaluate(
         "(s) => document.querySelector(`input[data-md-color-scheme=\"${s}\"]`).click()",
diff --git a/tests/test_accessibility_keyboard.py b/tests/test_accessibility_keyboard.py
index 8568457..ca8d057 100644
--- a/tests/test_accessibility_keyboard.py
+++ b/tests/test_accessibility_keyboard.py
@@ -2,8 +2,10 @@
 
 axe flags *markup* problems on a static snapshot. These tests use the keyboard the way a
 mouse-free user would: the skip link works, this repo's own interactive controls show a
-visible focus indicator, nothing hijacks tab order with a positive tabindex, and the palette
-toggle is reachable.
+visible focus indicator, and nothing hijacks tab order with a positive tabindex. The light/dark
+and Essentials/Advanced toggles are plugins now (mkdocs-light-dark-toggle,
+mkdocs-audience-toggle) — their own keyboard reachability is covered by each plugin's own test
+suite, not repeated here.
 
 Browser tier — same setup as test_accessibility_browser.py (`playwright install chromium`).
 """
@@ -58,36 +60,6 @@ def test_no_positive_tabindex(page, site_url, path):
     )
 
 
-def test_palette_toggle_is_keyboard_reachable(page, site_url):
-    """The dark/light toggle must be operable without a mouse. docs/javascripts/
-    theme_toggle.js replaces Material's native radios+labels with its own
-    `.pt-theme-option` buttons (a two-segment sun/moon control, matching the
-    Essentials/Advanced content-mode toggle) and hides the native form — so this checks the
-    *replacement* buttons are real, labeled, visible controls and that Tab reaches
-    one, rather than the native radios (which are now deliberately hidden)."""
-    page.goto(site_url)
-    buttons = page.evaluate(
-        """() => [...document.querySelectorAll('.pt-theme-option')].map((b) => ({
-            hidden: b.hasAttribute('hidden'),
-            display: getComputedStyle(b).display,
-            label: b.getAttribute('aria-label') || '',
-        }))"""
-    )
-    assert len(buttons) >= 2, "expected at least two theme option buttons (light + dark)"
-    assert all(not b["hidden"] and b["display"] != "none" for b in buttons), (
-        "a theme option button is hidden from keyboard/AT users entirely"
-    )
-    assert all(b["label"] for b in buttons), "a theme option button has no accessible name"
-
-    for _ in range(25):
-        page.keyboard.press("Tab")
-        if page.evaluate(
-            "() => document.activeElement?.classList.contains('pt-theme-option')"
-        ):
-            return
-    raise AssertionError("Tab never reached the theme toggle within 25 stops")
-
-
 # Interactive things this repo styles itself (as opposed to Material's header/search/palette
 # chrome, whose focus treatment is the theme's concern and is guarded statically by
 # test_accessibility.py). Each must paint an outline or box-shadow when focused from the
diff --git a/tests/test_content_mode_toggle.py b/tests/test_content_mode_toggle.py
index 354d483..f3e9d64 100644
--- a/tests/test_content_mode_toggle.py
+++ b/tests/test_content_mode_toggle.py
@@ -15,35 +15,35 @@
 
 def test_advanced_content_visible_by_default(page, site_url):
     page.goto(site_url)
-    mode = page.evaluate("() => document.documentElement.getAttribute('data-fcm-mode')")
+    mode = page.evaluate("() => document.documentElement.getAttribute('data-audience-mode')")
     assert mode == "advanced", "Advanced should be the default mode"
 
     # A row-level marker: the "sets" keyword-link row under Collections.
     hidden = page.evaluate(
         """() => {
-            const row = document.querySelector('p[data-fcm-hide~="essentials"]');
+            const row = document.querySelector('p[data-audience-hide~="essentials"]');
             return row ? getComputedStyle(row).display === 'none' : null;
         }"""
     )
-    assert hidden is False, "a data-fcm-hide=\"essentials\" row should be visible in Advanced"
+    assert hidden is False, "a data-audience-hide=\"essentials\" row should be visible in Advanced"
 
 
 def test_mode_query_param_hides_marked_row(page, site_url):
     page.goto(f"{site_url}/?mode=essentials")
-    mode = page.evaluate("() => document.documentElement.getAttribute('data-fcm-mode')")
+    mode = page.evaluate("() => document.documentElement.getAttribute('data-audience-mode')")
     assert mode == "essentials", "?mode=essentials should activate Essentials mode"
 
     hidden = page.evaluate(
         """() => {
-            const row = document.querySelector('p[data-fcm-hide~="essentials"]');
+            const row = document.querySelector('p[data-audience-hide~="essentials"]');
             return row ? getComputedStyle(row).display === 'none' : null;
         }"""
     )
-    assert hidden is True, "a data-fcm-hide=\"essentials\" row should be hidden once in Essentials mode"
+    assert hidden is True, "a data-audience-hide=\"essentials\" row should be hidden once in Essentials mode"
 
 
 def test_essentials_state_carries_to_content_page_heading_and_toc(page, site_url):
-    """functions.md's own '## Decorators { data-fcm-hide="essentials" }' heading (and its
+    """functions.md's own '## Decorators { data-audience-hide="essentials" }' heading (and its
     integrated-TOC entry) should hide too — carried over from the homepage's marker via
     localStorage, with no need to visit the homepage first in this same test."""
     page.goto(f"{site_url}/organization/functions/?mode=essentials")
@@ -107,13 +107,13 @@ def test_pfg_section_wrapper_is_hidden_with_its_heading(page, site_url):
 
 
 def test_whole_homepage_card_hides(page, site_url):
-    """A page with `cheatsheet_attrs: {data-fcm-hide: essentials}` in its front matter
+    """A page with `cheatsheet_attrs: {data-audience-hide: essentials}` in its front matter
     gets the marker on its cheatsheet card's <li>, which the audience toggle hides."""
     page.goto(f"{site_url}/?mode=essentials")
 
     card_display = page.evaluate(
         """() => {
-            const card = document.querySelector('.md-cheatsheet__card[data-fcm-hide~="essentials"]');
+            const card = document.querySelector('.md-cheatsheet__card[data-audience-hide~="essentials"]');
             return card ? getComputedStyle(card).display : null;
         }"""
     )
@@ -122,7 +122,7 @@ def test_whole_homepage_card_hides(page, site_url):
 
 def test_link_to_hidden_section_recovers_to_advanced(page, site_url):
     """collections.md's own cheat-sheet table (near the top) links to #tuples even
-    while the "Tuples" heading itself is hidden by data-fcm-hide="essentials" — clicking
+    while the "Tuples" heading itself is hidden by data-audience-hide="essentials" — clicking
     that visible link should flip the toggle back to Advanced and reveal the
     section, rather than landing on a hidden target and doing nothing."""
     page.goto(f"{site_url}/types/collections/?mode=essentials")
@@ -146,9 +146,9 @@ def test_link_to_hidden_section_recovers_to_advanced(page, site_url):
     after = page.evaluate(
         """() => ({
             tuplesDisplay: getComputedStyle(document.getElementById('tuples')).display,
-            mode: document.documentElement.getAttribute('data-fcm-mode'),
-            toggleActive: document.getElementById('fcm-toggle')?.dataset.active,
-            stored: localStorage.getItem('fcm-mode'),
+            mode: document.documentElement.getAttribute('data-audience-mode'),
+            toggleActive: document.getElementById('audience-toggle')?.dataset.active,
+            stored: localStorage.getItem('audience-mode'),
         })"""
     )
     assert after["tuplesDisplay"] != "none", "clicking the link should reveal the Tuples section"
@@ -172,6 +172,6 @@ def test_link_recovery_ignores_toc_links_to_visible_sections(page, site_url):
     lists_link.first.click()
 
     still_essentials = page.evaluate(
-        "() => document.documentElement.getAttribute('data-fcm-mode')"
+        "() => document.documentElement.getAttribute('data-audience-mode')"
     )
     assert still_essentials == "essentials", "a link to an already-visible section should not flip the mode"