diff --git a/book.toml b/book.toml
index 936e582..e2d91b3 100644
--- a/book.toml
+++ b/book.toml
@@ -21,6 +21,7 @@ edit-url-template = "https://github.com/KaiserY/trpl-zh-cn/edit/main/{path}"
 [output.typst-pdf]
 pdf = true
 section-number = true
+rust-book = true
 
 [rust]
 edition = "2021"
diff --git a/ferris.css b/ferris.css
index caa2ee7..513efa1 100644
--- a/ferris.css
+++ b/ferris.css
@@ -42,4 +42,26 @@ body.ayu .not_desired_behavior {
 
 .ferris-explain {
   width: 100px;
-}
\ No newline at end of file
+}
+
+/*
+  A bit of a hack to make small Ferris use the existing buttons container but
+  only show/hide the buttons on hover over the `pre`. Targeting `.listing`
+  increases the specificity of this rule.
+*/
+pre > .buttons {
+  visibility: visible;
+  opacity: 1;
+  transition: none;
+}
+
+pre > .buttons button {
+  visibility: hidden;
+  opacity: 0;
+  transition: visibility 0.1s linear, opacity 0.1s linear;
+}
+
+pre:hover > .buttons button {
+  visibility: visible;
+  opacity: 1;
+}
diff --git a/ferris.js b/ferris.js
index 4fd025e..13b1ceb 100644
--- a/ferris.js
+++ b/ferris.js
@@ -1,65 +1,102 @@
-var ferrisTypes = [
+// @ts-check
+
+/**
+ * @typedef {{ attr: string, title: string }} FerrisType
+ */
+
+/** @type {Array<FerrisType>} */
+const FERRIS_TYPES = [
   {
-    attr: 'does_not_compile',
-    title: '这段代码无法通过编译！'
+    attr: "does_not_compile",
+    title: "This code does not compile!",
   },
   {
-    attr: 'panics',
-    title: '这段代码会 Panic！'
+    attr: "panics",
+    title: "This code panics!",
   },
   {
-    attr: 'not_desired_behavior',
-    title: '这段代码的运行结果不符合预期。'
-  }
-]
+    attr: "not_desired_behavior",
+    title: "This code does not produce the desired behavior.",
+  },
+];
 
-document.addEventListener('DOMContentLoaded', () => {
-  for (var ferrisType of ferrisTypes) {
-    attachFerrises(ferrisType)
+document.addEventListener("DOMContentLoaded", () => {
+  for (let ferrisType of FERRIS_TYPES) {
+    attachFerrises(ferrisType);
   }
-})
+});
 
+/**
+ * @param {FerrisType} type
+ */
 function attachFerrises(type) {
-  var elements = document.getElementsByClassName(type.attr)
+  let elements = document.getElementsByClassName(type.attr);
 
-  for (var codeBlock of elements) {
-    var lines = codeBlock.innerText.replace(/\n$/, '').split(/\n/).length
-    var size = 'large'
-    if (lines < 4) {
-      size = 'small'
+  for (let codeBlock of elements) {
+    // Skip SVG etc.: in principle, these should never be attached to those, but
+    // this means if someone happens to have a browser extension which *is*
+    // attaching them, it will not break the code.
+    if (!(codeBlock instanceof HTMLElement)) {
+      continue;
     }
 
-    var container = prepareFerrisContainer(codeBlock, size == 'small')
-    container.appendChild(createFerris(type, size))
+    let codeLines = codeBlock.innerText;
+    let extra = codeLines.endsWith("\n") ? 1 : 0;
+    let numLines = codeLines.split("\n").length - extra;
+
+    /** @type {'small' | 'large'} */
+    let size = numLines < 4 ? "small" : "large";
+
+    let container = prepareFerrisContainer(codeBlock, size == "small");
+    if (!container) {
+      continue;
+    }
+
+    container.appendChild(createFerris(type, size));
   }
 }
 
+/**
+ * @param {HTMLElement} element - Code block element to attach a Ferris to.
+ * @param {boolean} useButtons - Whether to attach to existing buttons.
+ * @returns {Element | null} - The container element to use.
+ */
 function prepareFerrisContainer(element, useButtons) {
-  var foundButtons = element.parentElement.querySelector('.buttons')
+  let foundButtons = element.parentElement?.querySelector(".buttons");
   if (useButtons && foundButtons) {
-    return foundButtons
+    return foundButtons;
   }
 
-  var div = document.createElement('div')
-  div.classList.add('ferris-container')
+  let div = document.createElement("div");
+  div.classList.add("ferris-container");
 
-  element.parentElement.insertBefore(div, element)
+  if (!element.parentElement) {
+    console.error(`Could not install Ferris on ${element}, which is missing a parent`);
+    return null;
+  }
 
-  return div
+  element.parentElement.insertBefore(div, element);
+
+  return div;
 }
 
+/**
+ * @param {FerrisType} type
+ * @param {'small' | 'large'} size
+ * @returns {HTMLAnchorElement} - The generated anchor element.
+ */
 function createFerris(type, size) {
-  var a = document.createElement('a')
-  a.setAttribute('href', 'ch00-00-introduction.html#ferris')
-  a.setAttribute('target', '_blank')
+  let a = document.createElement("a");
+  a.setAttribute("href", "ch00-00-introduction.html#ferris");
+  a.setAttribute("target", "_blank");
 
-  var img = document.createElement('img')
-  img.setAttribute('src', 'img/ferris/' + type.attr + '.svg')
-  img.setAttribute('title', type.title)
-  img.classList.add('ferris')
-  img.classList.add('ferris-' + size)
+  let img = document.createElement("img");
+  img.setAttribute("src", "img/ferris/" + type.attr + ".svg");
+  img.setAttribute("title", type.title);
+  img.classList.add("ferris");
+  img.classList.add("ferris-" + size);
 
-  a.appendChild(img)
+  a.appendChild(img);
 
-  return a
-}
\ No newline at end of file
+  return a;
+}
diff --git a/theme/2018-edition.css b/theme/2018-edition.css
index b1dcf93..2276ccb 100644
--- a/theme/2018-edition.css
+++ b/theme/2018-edition.css
@@ -1,9 +1,9 @@
 span.caption {
-    font-size: .8em;
-    font-weight: 600;
+  font-size: 0.8em;
+  font-weight: 600;
 }
 
 span.caption code {
-    font-size: 0.875em;
-    font-weight: 400;
+  font-size: 0.875em;
+  font-weight: 400;
 }
diff --git a/theme/listing.css b/theme/listing.css
index 5998d39..40ae35a 100644
--- a/theme/listing.css
+++ b/theme/listing.css
@@ -1,8 +1,8 @@
 figure.listing {
-    margin: 0;
+  margin: 0;
 }
 
 .listing figcaption {
-    font-size: .8em;
-    font-weight: 600;
+  font-size: 0.8em;
+  font-weight: 600;
 }
diff --git a/theme/semantic-notes.css b/theme/semantic-notes.css
index 7e68eb3..b6852a0 100644
--- a/theme/semantic-notes.css
+++ b/theme/semantic-notes.css
@@ -4,10 +4,10 @@
   identical while updating the presentation.
 */
 .note {
-    margin: 20px 0;
-    padding: 0 20px;
-    color: var(--fg);
-    background-color: var(--quote-bg);
-    border-block-start: 0.1em solid var(--quote-border);
-    border-block-end: 0.1em solid var(--quote-border);
+  margin: 20px 0;
+  padding: 0 20px;
+  color: var(--fg);
+  background-color: var(--quote-bg);
+  border-block-start: 0.1em solid var(--quote-border);
+  border-block-end: 0.1em solid var(--quote-border);
 }