diff --git a/_pkgdown.yml b/_pkgdown.yml
index 78bbe7c..4d9aca7 100644
--- a/_pkgdown.yml
+++ b/_pkgdown.yml
@@ -15,7 +15,17 @@ navbar:
       text: News
       href: news/index.html
 
+# The articles are read as a book: chapter 1 is Get started, then the articles
+# below in this order, grouped into parts by `navbar`. The chapter panel, the
+# numbers and the previous / next links follow this list (pkgdown/extra.js).
+# A new chapter is one line in `contents`; a new part is one more entry with
+# `title`, `navbar`, `desc` and `contents`.
 articles:
+- title: Get started
+  navbar: ~
+  contents:
+  - randomPlantedForest
+
 - title: Understanding the model
   navbar: Understanding the model
   desc: What a fitted model is made of, and how the forest behind it is grown.
diff --git a/pkgdown/extra.css b/pkgdown/extra.css
index 8433173..63ed0ae 100644
--- a/pkgdown/extra.css
+++ b/pkgdown/extra.css
@@ -7,3 +7,120 @@
     hyphens: none;
   }
 }
+
+/* The articles as a book (see extra.js): section numbers, the chapter panel,
+   previous / next chapter. Colours come from Bootstrap's variables, so light
+   and dark mode both work. */
+.section-number {
+  margin-right: 0.5em;
+  color: var(--bs-secondary-color);
+  font-variant-numeric: tabular-nums;
+}
+.book-panel h2 { margin-top: 1.5rem; font-size: 1.25rem; }
+.book-panel ol { list-style: none; margin: 0; padding: 0; }
+.book-panel .book-part {
+  margin: 0.9rem 0 0.2rem 0.5rem;
+  font-size: 0.75rem;
+  font-weight: 600;
+  letter-spacing: 0.04em;
+  text-transform: uppercase;
+  color: var(--bs-secondary-color);
+}
+.book-panel .book-row { display: flex; align-items: flex-start; }
+.book-panel a {
+  display: flex;
+  flex: 1 1 auto;
+  gap: 0.5em;
+  padding: 0.25rem 0.5rem;
+  margin-bottom: 2px;
+  border-radius: var(--bs-border-radius);
+  color: inherit;
+  text-decoration: none;
+  line-height: 1.3;
+}
+.book-panel a:hover, .book-panel a:focus {
+  background-color: rgba(var(--bs-primary-rgb), 0.1);
+}
+.book-panel .book-num {
+  flex: 0 0 auto;
+  min-width: 1.2em;
+  color: var(--bs-secondary-color);
+  font-variant-numeric: tabular-nums;
+}
+.book-panel .book-chapter.current > .book-row > a {
+  font-weight: 600;
+  color: var(--bs-link-color);
+  background-color: rgba(var(--bs-primary-rgb), 0.08);
+}
+.book-panel code { font-size: 0.9em; padding: 0; background: none; color: inherit; }
+.book-panel .book-sections { margin-left: 0.75rem; font-size: 0.9em; }
+.book-panel .book-sections .book-sections { margin-left: 1rem; }
+.book-panel .book-sections .book-num { min-width: 2em; }
+.book-panel .book-sections .book-sections .book-num { min-width: 2.8em; }
+.book-panel .book-sections a.active {
+  background-color: rgba(var(--bs-body-color-rgb), 0.1);
+  font-weight: 600;
+}
+.book-panel .book-unfold {
+  flex: 0 0 auto;
+  width: 1.6rem;
+  height: 1.6rem;
+  margin-top: 0.1rem;
+  border: 0;
+  border-radius: var(--bs-border-radius);
+  background: none;
+  color: var(--bs-secondary-color);
+}
+.book-panel .book-unfold::before {
+  content: "";
+  display: inline-block;
+  border: solid currentColor;
+  border-width: 0 1.5px 1.5px 0;
+  padding: 2.5px;
+  transform: rotate(-45deg);
+  transition: transform 0.15s;
+}
+.book-panel .book-unfold[aria-expanded="true"]::before { transform: rotate(45deg); }
+.book-panel .book-unfold:hover { background-color: rgba(var(--bs-primary-rgb), 0.1); }
+
+/* Wide screens: the panel stays in view in the sidebar. */
+@media (min-width: 768px) {
+  .book-panel-side {
+    position: sticky;
+    top: 56px;
+    max-height: calc(100vh - 56px - 1rem);
+    overflow-y: auto;
+  }
+  .book-panel-phone { display: none; }
+}
+/* Phones: a collapsed "Chapters" box below the title, no sidebar. */
+@media (max-width: 767.98px) {
+  .row > aside.book-aside { display: none; }
+  .book-panel-phone {
+    margin: 0 0 1.5rem;
+    border: 1px solid var(--bs-border-color);
+    border-radius: var(--bs-border-radius);
+    background-color: rgba(var(--bs-body-color-rgb), 0.04);
+  }
+  .book-panel-phone > summary { padding: 0.5rem 0.75rem; font-weight: 600; }
+  .book-panel-phone .book-panel { padding: 0 0.5rem 0.5rem; }
+  .book-panel-phone .book-panel h2 { display: none; }
+}
+
+.book-pager {
+  display: flex;
+  justify-content: space-between;
+  gap: 1rem;
+  margin: 3rem 0 1rem;
+  padding-top: 1rem;
+  border-top: 1px solid var(--bs-border-color);
+}
+.book-pager a {
+  display: flex;
+  flex-direction: column;
+  max-width: 48%;
+  text-decoration: none;
+}
+.book-pager .book-pager-next { margin-left: auto; text-align: right; }
+.book-pager-label { font-size: 0.85em; color: var(--bs-secondary-color); }
+.book-pager-title { font-weight: 600; }
diff --git a/pkgdown/extra.js b/pkgdown/extra.js
new file mode 100644
index 0000000..7c84d26
--- /dev/null
+++ b/pkgdown/extra.js
@@ -0,0 +1,271 @@
+/* The articles as a book.
+
+   The chapters, their order and the parts are read from the navbar, which
+   pkgdown builds from `articles:` in _pkgdown.yml: chapter 1 is "Get started",
+   then every article of the Articles menu in order, grouped by the menu's
+   headings (the parts). Adding an article to `articles:` adds a chapter and
+   renumbers the ones after it; nothing here needs to change.
+
+   On a chapter page this script
+   - numbers the title and the section headings (5, 5.1, 5.1.1),
+   - shows the chapters in the right sidebar in place of "On this page", with
+     the current chapter's sections nested under it and the section in view
+     highlighted (on a phone, a collapsed "Chapters" box below the title),
+   - adds links to the previous and the next chapter at the bottom.
+   On the articles index it numbers the entries the same way. */
+(function () {
+  "use strict";
+
+  function pathOf(href) {
+    var p = new URL(href, document.baseURI).pathname;
+    return p.replace(/\/index\.html$/, "/").replace(/\.html$/, "");
+  }
+
+  function el(tag, attrs, children) {
+    var e = document.createElement(tag);
+    Object.keys(attrs || {}).forEach(function (k) {
+      if (k === "text") e.textContent = attrs[k];
+      else e.setAttribute(k, attrs[k]);
+    });
+    (children || []).forEach(function (c) { if (c) e.appendChild(c); });
+    return e;
+  }
+
+  /* The book: [{number, title, href, path, part}] in reading order. */
+  function readBook() {
+    var chapters = [];
+    var add = function (a, part) {
+      if (/\/articles\/(index\.html)?$/.test(new URL(a.href).pathname)) return;
+      chapters.push({ title: a.textContent.trim(), href: a.href, path: pathOf(a.href), part: part });
+    };
+    document.querySelectorAll("#navbar .navbar-nav > li > a.nav-link").forEach(function (a) {
+      if (/\/articles\/[^/]+\.html$/.test(new URL(a.href).pathname)) add(a, null);
+    });
+    var menu = document.querySelector('#dropdown-articles + .dropdown-menu');
+    var part = null;
+    if (menu) {
+      menu.querySelectorAll(".dropdown-header, a.dropdown-item").forEach(function (x) {
+        if (x.classList.contains("dropdown-header")) part = x.textContent.trim();
+        else add(x, part);
+      });
+    }
+    chapters.forEach(function (c, i) { c.number = i + 1; });
+    return chapters;
+  }
+
+  /* Number the section headings of a chapter page (or of a fetched one) and
+     return them as a tree [{number, title, id, children}]. */
+  function numberSections(root, chapter, edit) {
+    var tree = [];
+    var walk = function (container, level, prefix, into) {
+      var k = 0;
+      container.querySelectorAll(":scope > .section.level" + level).forEach(function (sec) {
+        var h = sec.querySelector(":scope > h" + level);
+        if (!h || h.hasAttribute("data-toc-skip")) return;
+        k += 1;
+        var number = prefix + "." + k;
+        var copy = h.cloneNode(true);
+        copy.querySelectorAll(".anchor, .section-number").forEach(function (x) { x.remove(); });
+        var node = { number: number, title: copy.innerHTML.trim(), id: sec.id || h.id, heading: h, children: [] };
+        if (edit) h.insertBefore(el("span", { class: "section-number", text: number }), h.firstChild);
+        into.push(node);
+        if (level < 3) walk(sec, level + 1, number, node.children);
+      });
+    };
+    var main = root.querySelector("main");
+    if (main) {
+      // the sections are children of main, or of a wrapper div
+      var top = main.querySelector(".section.level2");
+      if (top) walk(top.parentElement, 2, String(chapter.number), tree);
+    }
+    return tree;
+  }
+
+  function sectionList(nodes, href) {
+    if (!nodes.length) return null;
+    return el("ol", { class: "book-sections" }, nodes.map(function (n) {
+      var a = el("a", { href: href + "#" + n.id, "data-target": n.id }, [
+        el("span", { class: "book-num", text: n.number }),
+        el("span", { class: "book-title" })
+      ]);
+      a.lastChild.innerHTML = n.title; // the heading's own markup, e.g. <code>
+      return el("li", {}, [a, sectionList(n.children, href)]);
+    }));
+  }
+
+  function chapterLink(c, current) {
+    var a = el("a", { href: c.href, class: "book-chapter-link" }, [
+      el("span", { class: "book-num", text: String(c.number) }),
+      el("span", { class: "book-title", text: c.title })
+    ]);
+    if (current) a.setAttribute("aria-current", "page");
+    return a;
+  }
+
+  /* The other chapters' sections are read from their pages when asked for. */
+  var fetched = {};
+  function unfoldButton(c, li) {
+    var b = el("button", { type: "button", class: "book-unfold", "aria-expanded": "false",
+                           "aria-label": "Sections of chapter " + c.number });
+    b.addEventListener("click", function () {
+      var open = b.getAttribute("aria-expanded") === "true";
+      var list = li.querySelector(":scope > .book-sections");
+      if (open) {
+        b.setAttribute("aria-expanded", "false");
+        if (list) list.hidden = true;
+        return;
+      }
+      b.setAttribute("aria-expanded", "true");
+      if (list) { list.hidden = false; return; }
+      (fetched[c.path] = fetched[c.path] || fetch(c.href).then(function (r) {
+        if (!r.ok) throw new Error(r.status);
+        return r.text();
+      }).then(function (html) {
+        var doc = new DOMParser().parseFromString(html, "text/html");
+        return numberSections(doc, c, false);
+      })).then(function (tree) {
+        var ol = sectionList(tree, c.href);
+        if (ol) li.appendChild(ol);
+      }).catch(function () {
+        b.hidden = true;
+      });
+    });
+    return b;
+  }
+
+  function buildPanel(book, current, tree, idSuffix) {
+    var nav = el("nav", { class: "book-panel", "aria-label": "Chapters" });
+    var list = el("ol", { class: "book-chapters" });
+    var canFetch = location.protocol !== "file:";
+    var part;
+    book.forEach(function (c) {
+      if (c.part !== null && c.part !== part) {
+        list.appendChild(el("li", { class: "book-part", text: c.part }));
+      }
+      part = c.part;
+      var isCurrent = current && c.path === current.path;
+      var li = el("li", { class: "book-chapter" + (isCurrent ? " current" : "") });
+      var row = el("div", { class: "book-row" }, [chapterLink(c, isCurrent)]);
+      li.appendChild(row);
+      if (isCurrent) {
+        var ol = sectionList(tree, "");
+        if (ol) li.appendChild(ol);
+      } else if (canFetch) {
+        row.appendChild(unfoldButton(c, li));
+      }
+      list.appendChild(li);
+    });
+    nav.appendChild(el("h2", { text: "Chapters" }));
+    nav.appendChild(list);
+    return nav;
+  }
+
+  function pager(book, i) {
+    var prev = book[i - 1], next = book[i + 1];
+    var side = function (c, rel, label) {
+      if (!c) return el("span");
+      return el("a", { href: c.href, rel: rel, class: "book-pager-" + rel }, [
+        el("span", { class: "book-pager-label", text: label }),
+        el("span", { class: "book-pager-title", text: c.number + " " + c.title })
+      ]);
+    };
+    return el("nav", { class: "book-pager", "aria-label": "Previous and next chapter" }, [
+      side(prev, "prev", "← Previous chapter"),
+      side(next, "next", "Next chapter →")
+    ]);
+  }
+
+  /* Highlight the section in view, in every panel on the page. */
+  function spy(tree, panels) {
+    var flat = [];
+    (function f(ns) { ns.forEach(function (n) { flat.push(n); f(n.children); }); })(tree);
+    if (!flat.length) return;
+    var last = null;
+    var update = function () {
+      var cut = Math.max(100, window.innerHeight * 0.25);
+      var active = null;
+      flat.forEach(function (n) {
+        if (n.heading.getBoundingClientRect().top <= cut) active = n;
+      });
+      // at the end of the page, the last section counts as in view
+      var end = document.documentElement;
+      if (window.innerHeight + window.scrollY >= end.scrollHeight - 2) active = flat[flat.length - 1];
+      var id = active ? active.id : null;
+      if (id === last) return;
+      last = id;
+      panels.forEach(function (p) {
+        p.querySelectorAll("a[data-target]").forEach(function (a) {
+          var on = a.getAttribute("data-target") === id;
+          a.classList.toggle("active", on);
+          if (on && p.offsetParent !== null && p.scrollHeight > p.clientHeight) {
+            var top = a.offsetTop - p.offsetTop;
+            if (top < p.scrollTop || top > p.scrollTop + p.clientHeight - 40) {
+              p.scrollTop = top - p.clientHeight / 3;
+            }
+          }
+        });
+      });
+    };
+    var queued = false;
+    window.addEventListener("scroll", function () {
+      if (queued) return;
+      queued = true;
+      requestAnimationFrame(function () { queued = false; update(); });
+    }, { passive: true });
+    update();
+  }
+
+  function chapterPage(book, i) {
+    var c = book[i];
+    var main = document.querySelector("main#main");
+    var header = main.querySelector(".page-header");
+    var h1 = header && header.querySelector("h1");
+    if (h1) h1.insertBefore(el("span", { class: "section-number", text: String(c.number) }), h1.firstChild);
+    var tree = numberSections(document, c, true);
+
+    var aside = main.parentElement.querySelector(":scope > aside");
+    var panels = [];
+    if (aside) {
+      var toc = aside.querySelector("#toc");
+      if (toc) toc.hidden = true;
+      var side = buildPanel(book, c, tree);
+      side.classList.add("book-panel-side");
+      aside.insertBefore(side, aside.firstChild);
+      aside.classList.add("book-aside");
+      panels.push(side);
+    }
+    var box = el("details", { class: "book-panel-phone" }, [el("summary", { text: "Chapters" })]);
+    var phone = buildPanel(book, c, tree);
+    box.appendChild(phone);
+    box.addEventListener("click", function (e) {
+      if (e.target.closest && e.target.closest("a")) box.open = false;
+    });
+    if (header) header.after(box);
+    panels.push(phone);
+
+    main.appendChild(pager(book, i));
+    spy(tree, panels);
+  }
+
+  function indexPage(book) {
+    var byPath = {};
+    book.forEach(function (c) { byPath[c.path] = c; });
+    document.querySelectorAll("main#main dl dt a").forEach(function (a) {
+      var c = byPath[pathOf(a.href)];
+      if (!c) return;
+      var dt = a.closest("dt");
+      dt.insertBefore(el("span", { class: "section-number", text: String(c.number) }), dt.firstChild);
+      dt.classList.add("book-entry");
+    });
+  }
+
+  document.addEventListener("DOMContentLoaded", function () {
+    var book = readBook();
+    if (!book.length) return;
+    var here = pathOf(location.href);
+    for (var i = 0; i < book.length; i++) {
+      if (book[i].path === here) return chapterPage(book, i);
+    }
+    if (document.querySelector(".template-article-index")) indexPage(book);
+  });
+})();
diff --git a/vignettes/randomPlantedForest.Rmd b/vignettes/randomPlantedForest.Rmd
index aaf6deb..901777c 100644
--- a/vignettes/randomPlantedForest.Rmd
+++ b/vignettes/randomPlantedForest.Rmd
@@ -1,5 +1,8 @@
 ---
 title: "Getting Started with randomPlantedForest"
+description: >
+  A first model, its predictions and components, classification, and the
+  settings you may want.
 output: rmarkdown::html_vignette
 vignette: >
   %\VignetteIndexEntry{Getting Started with randomPlantedForest}