diff --git a/site/content/tutorial/10-transitions/02-adding-parameters/app-a/App.svelte b/site/content/tutorial/10-transitions/02-adding-parameters-to-transitions/app-a/App.svelte
similarity index 100%
rename from site/content/tutorial/10-transitions/02-adding-parameters/app-a/App.svelte
rename to site/content/tutorial/10-transitions/02-adding-parameters-to-transitions/app-a/App.svelte
diff --git a/site/content/tutorial/10-transitions/02-adding-parameters/app-b/App.svelte b/site/content/tutorial/10-transitions/02-adding-parameters-to-transitions/app-b/App.svelte
similarity index 100%
rename from site/content/tutorial/10-transitions/02-adding-parameters/app-b/App.svelte
rename to site/content/tutorial/10-transitions/02-adding-parameters-to-transitions/app-b/App.svelte
diff --git a/site/content/tutorial/10-transitions/02-adding-parameters/text.md b/site/content/tutorial/10-transitions/02-adding-parameters-to-transitions/text.md
similarity index 100%
rename from site/content/tutorial/10-transitions/02-adding-parameters/text.md
rename to site/content/tutorial/10-transitions/02-adding-parameters-to-transitions/text.md
diff --git a/site/content/tutorial/11-animations/01-animate/app-a/App.svelte b/site/content/tutorial/11-animations/01-animate/app-a/App.svelte
new file mode 100644
index 0000000000..c46096c204
--- /dev/null
+++ b/site/content/tutorial/11-animations/01-animate/app-a/App.svelte
@@ -0,0 +1,146 @@
+<script>
+	import { quintOut } from 'svelte/easing';
+	import crossfade from './crossfade.js'; // TODO put this in svelte/transition!
+
+	const { send, receive } = crossfade({
+		fallback(node, params) {
+			const style = getComputedStyle(node);
+			const transform = style.transform === 'none' ? '' : style.transform;
+
+			return {
+				duration: 600,
+				easing: quintOut,
+				css: t => `
+					transform: ${transform} scale(${t});
+					opacity: ${t}
+				`
+			};
+		}
+	});
+
+	let todos = [
+		{ id: 1, done: false, description: 'write some docs' },
+		{ id: 2, done: false, description: 'start writing JSConf talk' },
+		{ id: 3, done: true, description: 'buy some milk' },
+		{ id: 4, done: false, description: 'mow the lawn' },
+		{ id: 5, done: false, description: 'feed the turtle' },
+		{ id: 6, done: false, description: 'fix some bugs' },
+	];
+
+	let uid = todos.length + 1;
+
+	function add(input) {
+		const todo = {
+			id: uid++,
+			done: false,
+			description: input.value
+		};
+
+		todos = [todo, ...todos];
+		input.value = '';
+	}
+
+	function remove(todo) {
+		todos = todos.filter(t => t !== todo);
+	}
+
+	function handleKeydown(event) {
+		if (event.which === 13) {
+			addTodo(event.target);
+		}
+	}
+</script>
+
+<style>
+	.new-todo {
+		font-size: 1.4em;
+		width: 100%;
+		margin: 2em 0 1em 0;
+	}
+
+	.board {
+		max-width: 36em;
+		margin: 0 auto;
+	}
+
+	.left, .right {
+		float: left;
+		width: 50%;
+		padding: 0 1em 0 0;
+		box-sizing: border-box;
+	}
+
+	h2 {
+		font-size: 2em;
+		font-weight: 200;
+		user-select: none;
+	}
+
+	label {
+		top: 0;
+		left: 0;
+		display: block;
+		font-size: 1em;
+		line-height: 1;
+		padding: 0.5em;
+		margin: 0 auto 0.5em auto;
+		border-radius: 2px;
+		background-color: #eee;
+		user-select: none;
+	}
+
+	input { margin: 0 }
+
+	.right label {
+		background-color: rgb(180,240,100);
+	}
+
+	button {
+		float: right;
+		height: 1em;
+		box-sizing: border-box;
+		padding: 0 0.5em;
+		line-height: 1;
+		background-color: transparent;
+		border: none;
+		color: rgb(170,30,30);
+		opacity: 0;
+		transition: opacity 0.2s;
+	}
+
+	label:hover button {
+		opacity: 1;
+	}
+</style>
+
+<div class='board'>
+	<input class="new-todo" placeholder="what needs to be done?" on:enter={add}>
+
+	<div class='left'>
+		<h2>todo</h2>
+		{#each todos.filter(t => !t.done) as todo (todo.id)}
+			<label
+				in:receive="{{key: todo.id}}"
+				out:send="{{key: todo.id}}"
+			>
+				<input type=checkbox bind:checked={todo.done}>
+				{todo.description}
+				<button on:click="{() => remove(todo)}">x</button>
+			</label>
+		{/each}
+	</div>
+
+	<div class='right'>
+		<h2>done</h2>
+		{#each todos.filter(t => t.done) as todo (todo.id)}
+			<label
+				in:receive="{{key: todo.id}}"
+				out:send="{{key: todo.id}}"
+			>
+				<input type=checkbox bind:checked={todo.done}>
+				{todo.description}
+				<button on:click="{() => remove(todo)}">x</button>
+			</label>
+		{/each}
+	</div>
+</div>
\ No newline at end of file
diff --git a/site/content/tutorial/11-animations/01-animate/app-a/crossfade.js b/site/content/tutorial/11-animations/01-animate/app-a/crossfade.js
new file mode 100644
index 0000000000..e11e18b60e
--- /dev/null
+++ b/site/content/tutorial/11-animations/01-animate/app-a/crossfade.js
@@ -0,0 +1,65 @@
+import { quintOut } from 'svelte/easing';
+
+export default function crossfade({ send, receive, fallback }) {
+	let requested = new Map();
+	let provided = new Map();
+
+	function crossfade(from, node) {
+		const to = node.getBoundingClientRect();
+		const dx = from.left - to.left;
+		const dy = from.top - to.top;
+
+		const style = getComputedStyle(node);
+		const transform = style.transform === 'none' ? '' : style.transform;
+
+		return {
+			duration: 400,
+			easing: quintOut,
+			css: (t, u) => `
+				opacity: ${t};
+				transform: ${transform} translate(${u * dx}px,${u * dy}px);
+			`
+		};
+	}
+
+	return {
+		send(node, params) {
+			provided.set(params.key, {
+				rect: node.getBoundingClientRect()
+			});
+
+			return () => {
+				if (requested.has(params.key)) {
+					const { rect } = requested.get(params.key);
+					requested.delete(params.key);
+
+					return crossfade(rect, node);
+				}
+
+				// if the node is disappearing altogether
+				// (i.e. wasn't claimed by the other list)
+				// then we need to supply an outro
+				provided.delete(params.key);
+				return fallback(node, params);
+			};
+		},
+
+		receive(node, params) {
+			requested.set(params.key, {
+				rect: node.getBoundingClientRect()
+			});
+
+			return () => {
+				if (provided.has(params.key)) {
+					const { rect } = provided.get(params.key);
+					provided.delete(params.key);
+
+					return crossfade(rect, node);
+				}
+
+				requested.delete(params.key);
+				return fallback(node, params);
+			};
+		}
+	};
+}
\ No newline at end of file
diff --git a/site/content/tutorial/11-animations/01-animate/app-b/App.svelte b/site/content/tutorial/11-animations/01-animate/app-b/App.svelte
new file mode 100644
index 0000000000..c46096c204
--- /dev/null
+++ b/site/content/tutorial/11-animations/01-animate/app-b/App.svelte
@@ -0,0 +1,146 @@
+<script>
+	import { quintOut } from 'svelte/easing';
+	import crossfade from './crossfade.js'; // TODO put this in svelte/transition!
+
+	const { send, receive } = crossfade({
+		fallback(node, params) {
+			const style = getComputedStyle(node);
+			const transform = style.transform === 'none' ? '' : style.transform;
+
+			return {
+				duration: 600,
+				easing: quintOut,
+				css: t => `
+					transform: ${transform} scale(${t});
+					opacity: ${t}
+				`
+			};
+		}
+	});
+
+	let todos = [
+		{ id: 1, done: false, description: 'write some docs' },
+		{ id: 2, done: false, description: 'start writing JSConf talk' },
+		{ id: 3, done: true, description: 'buy some milk' },
+		{ id: 4, done: false, description: 'mow the lawn' },
+		{ id: 5, done: false, description: 'feed the turtle' },
+		{ id: 6, done: false, description: 'fix some bugs' },
+	];
+
+	let uid = todos.length + 1;
+
+	function add(input) {
+		const todo = {
+			id: uid++,
+			done: false,
+			description: input.value
+		};
+
+		todos = [todo, ...todos];
+		input.value = '';
+	}
+
+	function remove(todo) {
+		todos = todos.filter(t => t !== todo);
+	}
+
+	function handleKeydown(event) {
+		if (event.which === 13) {
+			addTodo(event.target);
+		}
+	}
+</script>
+
+<style>
+	.new-todo {
+		font-size: 1.4em;
+		width: 100%;
+		margin: 2em 0 1em 0;
+	}
+
+	.board {
+		max-width: 36em;
+		margin: 0 auto;
+	}
+
+	.left, .right {
+		float: left;
+		width: 50%;
+		padding: 0 1em 0 0;
+		box-sizing: border-box;
+	}
+
+	h2 {
+		font-size: 2em;
+		font-weight: 200;
+		user-select: none;
+	}
+
+	label {
+		top: 0;
+		left: 0;
+		display: block;
+		font-size: 1em;
+		line-height: 1;
+		padding: 0.5em;
+		margin: 0 auto 0.5em auto;
+		border-radius: 2px;
+		background-color: #eee;
+		user-select: none;
+	}
+
+	input { margin: 0 }
+
+	.right label {
+		background-color: rgb(180,240,100);
+	}
+
+	button {
+		float: right;
+		height: 1em;
+		box-sizing: border-box;
+		padding: 0 0.5em;
+		line-height: 1;
+		background-color: transparent;
+		border: none;
+		color: rgb(170,30,30);
+		opacity: 0;
+		transition: opacity 0.2s;
+	}
+
+	label:hover button {
+		opacity: 1;
+	}
+</style>
+
+<div class='board'>
+	<input class="new-todo" placeholder="what needs to be done?" on:enter={add}>
+
+	<div class='left'>
+		<h2>todo</h2>
+		{#each todos.filter(t => !t.done) as todo (todo.id)}
+			<label
+				in:receive="{{key: todo.id}}"
+				out:send="{{key: todo.id}}"
+			>
+				<input type=checkbox bind:checked={todo.done}>
+				{todo.description}
+				<button on:click="{() => remove(todo)}">x</button>
+			</label>
+		{/each}
+	</div>
+
+	<div class='right'>
+		<h2>done</h2>
+		{#each todos.filter(t => t.done) as todo (todo.id)}
+			<label
+				in:receive="{{key: todo.id}}"
+				out:send="{{key: todo.id}}"
+			>
+				<input type=checkbox bind:checked={todo.done}>
+				{todo.description}
+				<button on:click="{() => remove(todo)}">x</button>
+			</label>
+		{/each}
+	</div>
+</div>
\ No newline at end of file
diff --git a/site/content/tutorial/11-animations/01-animate/app-b/crossfade.js b/site/content/tutorial/11-animations/01-animate/app-b/crossfade.js
new file mode 100644
index 0000000000..e11e18b60e
--- /dev/null
+++ b/site/content/tutorial/11-animations/01-animate/app-b/crossfade.js
@@ -0,0 +1,65 @@
+import { quintOut } from 'svelte/easing';
+
+export default function crossfade({ send, receive, fallback }) {
+	let requested = new Map();
+	let provided = new Map();
+
+	function crossfade(from, node) {
+		const to = node.getBoundingClientRect();
+		const dx = from.left - to.left;
+		const dy = from.top - to.top;
+
+		const style = getComputedStyle(node);
+		const transform = style.transform === 'none' ? '' : style.transform;
+
+		return {
+			duration: 400,
+			easing: quintOut,
+			css: (t, u) => `
+				opacity: ${t};
+				transform: ${transform} translate(${u * dx}px,${u * dy}px);
+			`
+		};
+	}
+
+	return {
+		send(node, params) {
+			provided.set(params.key, {
+				rect: node.getBoundingClientRect()
+			});
+
+			return () => {
+				if (requested.has(params.key)) {
+					const { rect } = requested.get(params.key);
+					requested.delete(params.key);
+
+					return crossfade(rect, node);
+				}
+
+				// if the node is disappearing altogether
+				// (i.e. wasn't claimed by the other list)
+				// then we need to supply an outro
+				provided.delete(params.key);
+				return fallback(node, params);
+			};
+		},
+
+		receive(node, params) {
+			requested.set(params.key, {
+				rect: node.getBoundingClientRect()
+			});
+
+			return () => {
+				if (provided.has(params.key)) {
+					const { rect } = provided.get(params.key);
+					provided.delete(params.key);
+
+					return crossfade(rect, node);
+				}
+
+				requested.delete(params.key);
+				return fallback(node, params);
+			};
+		}
+	};
+}
\ No newline at end of file
diff --git a/site/content/tutorial/11-animations/01-animate/text.md b/site/content/tutorial/11-animations/01-animate/text.md
new file mode 100644
index 0000000000..7b8268e37b
--- /dev/null
+++ b/site/content/tutorial/11-animations/01-animate/text.md
@@ -0,0 +1,5 @@
+---
+title: The animate directive
+---
+
+TODO fix https://github.com/sveltejs/svelte/issues/2159 before working on `animate`
\ No newline at end of file
diff --git a/site/content/tutorial/11-animations/meta.json b/site/content/tutorial/11-animations/meta.json
new file mode 100644
index 0000000000..c71301495e
--- /dev/null
+++ b/site/content/tutorial/11-animations/meta.json
@@ -0,0 +1,3 @@
+{
+	"title": "Animations"
+}
\ No newline at end of file
diff --git a/site/content/tutorial/12-actions/01-actions/app-a/App.svelte b/site/content/tutorial/12-actions/01-actions/app-a/App.svelte
new file mode 100644
index 0000000000..cbd1f81282
--- /dev/null
+++ b/site/content/tutorial/12-actions/01-actions/app-a/App.svelte
@@ -0,0 +1,47 @@
+<script>
+	import { spring } from 'svelte/motion';
+
+	const coords = spring({ x: 0, y: 0 }, {
+		stiffness: 0.2,
+		damping: 0.4
+	});
+
+	function handlePanStart() {
+		coords.stiffness = coords.damping = 1;
+	}
+
+	function handlePanMove(event) {
+		coords.update($coords => ({
+			x: $coords.x + event.detail.dx,
+			y: $coords.y + event.detail.dy
+		}));
+	}
+
+	function handlePanEnd(event) {
+		coords.stiffness = 0.2;
+		coords.damping = 0.4;
+		coords.set({ x: 0, y: 0 });
+	}
+</script>
+
+<style>
+	.box {
+		--width: 100px;
+		--height: 100px;
+		position: absolute;
+		width: var(--width);
+		height: var(--height);
+		left: calc(50% - var(--width) / 2);
+		top: calc(50% - var(--height) / 2);
+		border-radius: 4px;
+		background-color: #ff3e00;
+		cursor: move;
+	}
+</style>
+
+<div class="box"
+	on:panstart={handlePanStart}
+	on:panmove={handlePanMove}
+	on:panend={handlePanEnd}
+	style="transform: translate({$coords.x}px,{$coords.y}px)"
+></div>
\ No newline at end of file
diff --git a/site/content/tutorial/12-actions/01-actions/app-a/pannable.js b/site/content/tutorial/12-actions/01-actions/app-a/pannable.js
new file mode 100644
index 0000000000..332cd3e147
--- /dev/null
+++ b/site/content/tutorial/12-actions/01-actions/app-a/pannable.js
@@ -0,0 +1,9 @@
+export function pannable(node) {
+	// setup work goes here...
+
+	return {
+		destroy() {
+			// ...cleanup goes here
+		}
+	};
+}
\ No newline at end of file
diff --git a/site/content/tutorial/12-actions/01-actions/app-b/App.svelte b/site/content/tutorial/12-actions/01-actions/app-b/App.svelte
new file mode 100644
index 0000000000..1324277bac
--- /dev/null
+++ b/site/content/tutorial/12-actions/01-actions/app-b/App.svelte
@@ -0,0 +1,49 @@
+<script>
+	import { spring } from 'svelte/motion';
+	import { pannable } from './pannable.js';
+
+	const coords = spring({ x: 0, y: 0 }, {
+		stiffness: 0.2,
+		damping: 0.4
+	});
+
+	function handlePanStart() {
+		coords.stiffness = coords.damping = 1;
+	}
+
+	function handlePanMove(event) {
+		coords.update($coords => ({
+			x: $coords.x + event.detail.dx,
+			y: $coords.y + event.detail.dy
+		}));
+	}
+
+	function handlePanEnd(event) {
+		coords.stiffness = 0.2;
+		coords.damping = 0.4;
+		coords.set({ x: 0, y: 0 });
+	}
+</script>
+
+<style>
+	.box {
+		--width: 100px;
+		--height: 100px;
+		position: absolute;
+		width: var(--width);
+		height: var(--height);
+		left: calc(50% - var(--width) / 2);
+		top: calc(50% - var(--height) / 2);
+		border-radius: 4px;
+		background-color: #ff3e00;
+		cursor: move;
+	}
+</style>
+
+<div class="box"
+	use:pannable
+	on:panstart={handlePanStart}
+	on:panmove={handlePanMove}
+	on:panend={handlePanEnd}
+	style="transform: translate({$coords.x}px,{$coords.y}px)"
+></div>
\ No newline at end of file
diff --git a/site/content/tutorial/12-actions/01-actions/app-b/pannable.js b/site/content/tutorial/12-actions/01-actions/app-b/pannable.js
new file mode 100644
index 0000000000..f7d15328be
--- /dev/null
+++ b/site/content/tutorial/12-actions/01-actions/app-b/pannable.js
@@ -0,0 +1,47 @@
+export function pannable(node) {
+	let x;
+	let y;
+
+	function handleMousedown(event) {
+		x = event.clientX;
+		y = event.clientY;
+
+		node.dispatchEvent(new CustomEvent('panstart', {
+			detail: { x, y }
+		}));
+
+		window.addEventListener('mousemove', handleMousemove);
+		window.addEventListener('mouseup', handleMouseup);
+	}
+
+	function handleMousemove(event) {
+		const dx = event.clientX - x;
+		const dy = event.clientY - y;
+		x = event.clientX;
+		y = event.clientY;
+
+		node.dispatchEvent(new CustomEvent('panmove', {
+			detail: { x, y, dx, dy }
+		}));
+	}
+
+	function handleMouseup(event) {
+		x = event.clientX;
+		y = event.clientY;
+
+		node.dispatchEvent(new CustomEvent('panend', {
+			detail: { x, y }
+		}));
+
+		window.removeEventListener('mousemove', handleMousemove);
+		window.removeEventListener('mouseup', handleMouseup);
+	}
+
+	node.addEventListener('mousedown', handleMousedown);
+
+	return {
+		destroy() {
+			node.removeEventListener('mousedown', handleMousedown);
+		}
+	};
+}
\ No newline at end of file
diff --git a/site/content/tutorial/12-actions/01-actions/text.md b/site/content/tutorial/12-actions/01-actions/text.md
new file mode 100644
index 0000000000..279dc3123f
--- /dev/null
+++ b/site/content/tutorial/12-actions/01-actions/text.md
@@ -0,0 +1,87 @@
+---
+title: The use directive
+---
+
+Actions are essentially element-level lifecycle functions. They're useful for things like:
+
+* interfacing with third-party libraries
+* lazy-loaded images
+* tooltips
+* adding custom event handlers
+
+In this app, we want to make the orange box 'pannable'. It has event handlers for the `panstart`, `panmove` and `panend` events, but these aren't native DOM events. We have to dispatch them ourselves. First, import the `pannable` function...
+
+```js
+import { pannable } from './pannable.js';
+```
+
+...then use it with the element:
+
+```html
+<div class="box"
+	use:pannable
+	on:panstart={handlePanStart}
+	on:panmove={handlePanMove}
+	on:panend={handlePanEnd}
+	style="transform: translate({$coords.x}px,{$coords.y}px)"
+></div>
+```
+
+Open the `pannable.js` file. Like transition functions, an action function receives a `node` and some optional parameters, and returns an action object. That object must have a `destroy` function, which is called when the element is unmounted.
+
+We want to fire `panstart` event when the user mouses down on the element, `panmove` events (with `dx` and `dy` properties showing how far the mouse moved) when they drag it, and `panend` events when they mouse up. One possible implementation looks like this:
+
+```js
+export function pannable(node) {
+	let x;
+	let y;
+
+	function handleMousedown(event) {
+		x = event.clientX;
+		y = event.clientY;
+
+		node.dispatchEvent(new CustomEvent('panstart', {
+			detail: { x, y }
+		}));
+
+		window.addEventListener('mousemove', handleMousemove);
+		window.addEventListener('mouseup', handleMouseup);
+	}
+
+	function handleMousemove(event) {
+		const dx = event.clientX - x;
+		const dy = event.clientY - y;
+		x = event.clientX;
+		y = event.clientY;
+
+		node.dispatchEvent(new CustomEvent('panmove', {
+			detail: { x, y, dx, dy }
+		}));
+	}
+
+	function handleMouseup(event) {
+		x = event.clientX;
+		y = event.clientY;
+
+		node.dispatchEvent(new CustomEvent('panend', {
+			detail: { x, y }
+		}));
+
+		window.removeEventListener('mousemove', handleMousemove);
+		window.removeEventListener('mouseup', handleMouseup);
+	}
+
+	node.addEventListener('mousedown', handleMousedown);
+
+	return {
+		destroy() {
+			node.removeEventListener('mousedown', handleMousedown);
+		}
+	};
+}
+```
+
+Update the `pannable` function and try moving the box around.
+
+> This implementation is for demonstration purposes — a more complete one would also consider touch events.
+
diff --git a/site/content/tutorial/12-actions/02-adding-parameters-to-actions/app-a/App.svelte b/site/content/tutorial/12-actions/02-adding-parameters-to-actions/app-a/App.svelte
new file mode 100644
index 0000000000..30404ce4c5
--- /dev/null
+++ b/site/content/tutorial/12-actions/02-adding-parameters-to-actions/app-a/App.svelte
@@ -0,0 +1 @@
+TODO
\ No newline at end of file
diff --git a/site/content/tutorial/12-actions/02-adding-parameters-to-actions/app-b/App.svelte b/site/content/tutorial/12-actions/02-adding-parameters-to-actions/app-b/App.svelte
new file mode 100644
index 0000000000..30404ce4c5
--- /dev/null
+++ b/site/content/tutorial/12-actions/02-adding-parameters-to-actions/app-b/App.svelte
@@ -0,0 +1 @@
+TODO
\ No newline at end of file
diff --git a/site/content/tutorial/12-actions/02-adding-parameters-to-actions/text.md b/site/content/tutorial/12-actions/02-adding-parameters-to-actions/text.md
new file mode 100644
index 0000000000..5631bebbc5
--- /dev/null
+++ b/site/content/tutorial/12-actions/02-adding-parameters-to-actions/text.md
@@ -0,0 +1,5 @@
+---
+title: Adding parameters
+---
+
+TODO example with Prism highlighting
\ No newline at end of file
diff --git a/site/content/tutorial/12-actions/meta.json b/site/content/tutorial/12-actions/meta.json
new file mode 100644
index 0000000000..a154610283
--- /dev/null
+++ b/site/content/tutorial/12-actions/meta.json
@@ -0,0 +1,3 @@
+{
+	"title": "Actions"
+}
\ No newline at end of file
diff --git a/site/content/tutorial/99-todo/99-todo/text.md b/site/content/tutorial/99-todo/99-todo/text.md
index 93cbdb6121..17c4cbb5e2 100644
--- a/site/content/tutorial/99-todo/99-todo/text.md
+++ b/site/content/tutorial/99-todo/99-todo/text.md
@@ -85,6 +85,7 @@ Maybe lifecycle should go first, since we're using `onMount` in the `this` demo?
 * [ ] custom stores
 * [ ] `bind:value={$foo}`
 * [ ] `$foo += 1` (if we implement it)
+* [ ] Adapting Immer, Redux, Microstates, xstate etc
 
 
 ## Motion
@@ -119,7 +120,7 @@ Maybe lifecycle should go first, since we're using `onMount` in the `this` demo?
 
 ## use: directive
 
-* [ ] `use:foo`
+* [x] `use:foo`
 * [ ] `use:foo={bar}`
 
 ## class: directive
diff --git a/site/src/routes/tutorial/[slug]/index.svelte b/site/src/routes/tutorial/[slug]/index.svelte
index 082c9a98bc..23222045d2 100644
--- a/site/src/routes/tutorial/[slug]/index.svelte
+++ b/site/src/routes/tutorial/[slug]/index.svelte
@@ -89,7 +89,7 @@
 	function handle_change(event) {
 		completed = event.detail.components.every((file, i) => {
 			const expected = chapter.app_b[i];
-			return (
+			return expected && (
 				file.name === expected.name &&
 				file.type === expected.type &&
 				file.source === expected.source