# A Japanese drill with the answers upside down

> Two pages of a Japanese drill series, arithmetic across and kanji in columns, each exercise followed by its answers printed upside down.

- HTML version: https://postext.dev/en/cookbook/japanese-drill-upside-down-answers
- Recipe Nº 172 · Textbooks · Level 2 (Intermediate) · Outputs: Canvas, PDF
- Genres: Workbooks & exercises, Textbooks
- Requires postext ≥ 1.59.0, postext-pdf ≥ 1.59.0 · tested with 1.59.0, postext-pdf 1.59.0 on 2026-10-24
- Pages: [1](https://postext.dev/cookbook/japanese-drill-upside-down-answers/ja/p01.webp?v=4fd772fe), [2](https://postext.dev/cookbook/japanese-drill-upside-down-answers/ja/p02.webp?v=4fd772fe), [1](https://postext.dev/cookbook/japanese-drill-upside-down-answers/ja/p03.webp?v=4fd772fe), [2](https://postext.dev/cookbook/japanese-drill-upside-down-answers/ja/p04.webp?v=4fd772fe)
- Open in Sandbox: https://postext.dev/en/sandbox#recipe=japanese-drill-upside-down-answers&lang=ja (.postext: https://postext.dev/cookbook/japanese-drill-upside-down-answers/ja/japanese-drill-upside-down-answers.postext)
- Last updated: 2026-10-24
- Other languages: [es](https://postext.dev/es/cookbook/japanese-drill-upside-down-answers.md), [ca](https://postext.dev/ca/cookbook/japanese-drill-upside-down-answers.md), [de](https://postext.dev/de/cookbook/japanese-drill-upside-down-answers.md), [fr](https://postext.dev/fr/cookbook/japanese-drill-upside-down-answers.md), [it](https://postext.dev/it/cookbook/japanese-drill-upside-down-answers.md), [pt](https://postext.dev/pt/cookbook/japanese-drill-upside-down-answers.md), [zh](https://postext.dev/zh/cookbook/japanese-drill-upside-down-answers.md), [ja](https://postext.dev/ja/cookbook/japanese-drill-upside-down-answers.md), [ar](https://postext.dev/ar/cookbook/japanese-drill-upside-down-answers.md)

## In short

A Japanese school drill book: sums, number boxes, choices and true-or-false on one page, kanji and readings on another, set top to bottom. Under every exercise its answers are printed upside down, so a child turns the book to check.

## What you'll build

Two pages from a third-year drill series on B5. The arithmetic page runs across: a pale blue band with the subject badge, the title and a tanuki mascot, a name line and a score box, then ひっ算 with a box for each digit of the answer, number boxes after six sums, ア イ ウ choices in a row, ○× statements with a bracket at the end of the line and two word problems with lines to write the working on. The kanji page is set the way a 国語 drill is printed, top to bottom and right to left: readings with a box for the kanji, lined words whose reading goes in brackets, choices to ring and a meaning to pick. Under every exercise, its answers are printed upside down in small grey type. A child sees where they are, cannot read them at a glance, and turns the book round to check.

**This recipe answers:**

- How do I print the answers upside down under each exercise of a Japanese drill?
- How do I set a Japanese drill page in vertical columns with the same exercise design as the horizontal one?
- How do I set long division the way each country's schools write it?

## The short answer

The answers printed upside down under each exercise.

```js
// script.js, lines 35–55
// `placement: 'inverted'` sets each exercise's key right after it in a box turned 180°: the
// pupil sees where the answers are without reading them, and turns the book to check. The
// key's words come from the exercise (the options' katakana, ○ and ×, the operations), so
// the Markdown holds nothing twice.
const drill = {
  id: 'drill',
  number: { shape: 'square', fontFamily: TEXT, fontWeight: 600, background: col('blue') },
  instruction: { fontFamily: ROUND, bold: false },
  options: { layout: 'row' }, // ア イ ウ side by side (the default labels in Japanese)
  trueFalse: { look: 'bracket' }, // （　） for ○ or ×
  blank: { look: 'box', width: 'answer', color: col('rule') }, // □ to write in
  area: { kind: 'lines', color: col('rule') },
  grid: { rule: col('rule') },
  solutions: { placement: 'inverted', box: 'kotae' },
  marginTop: em(1.1), marginBottom: em(0.4),
};
const kotae = { id: 'kotae', title: '', backgroundEnabled: false, border: { enabled: false },
  padding: { top: pt(0), right: pt(0), bottom: pt(0), left: pt(0) },
  body: { fontFamily: ROUND, fontSize: pt(8), lineHeight: pt(12), color: col('muted'),
    firstLineIndent: pt(0) },
  marginTop: mm(1), marginBottom: mm(2), keepTogether: true };
```

## Ingredients

**Teaches**

- [Solutions](https://postext.dev/en/docs/exercises.md#solutions): Where the answers print: none, after each exercise, upside down at its foot, at the end of the chapter, or where a :::solutions line stands; a key made from the answers and the :::solution of each exercise.
- [Exercise styles](https://postext.dev/en/docs/exercises.md#exercise-styles): exerciseStyles: how a family of exercises prints — the number (disc, square, label), the instruction, option labels, blanks, true/false boxes, dots to join, the word bank, writing areas, grids, activity icons and difficulty marks.
- [Vertical text](https://postext.dev/en/docs/configuration-page-layout.md#vertical-writing): Chinese and Japanese set top to bottom in lines read from the right (layout.writingMode 'vertical-rl'), with columns as tiers, figures and tables standing upright and punctuation in its vertical forms.

**Also uses**

- [Exercises](https://postext.dev/en/docs/exercises.md#exercises)
- [Operations in columns](https://postext.dev/en/docs/exercises.md#operations-in-columns)
- [Gaps and word banks](https://postext.dev/en/docs/exercises.md#gaps-and-word-banks)
- [Choice and true or false](https://postext.dev/en/docs/exercises.md#choice-and-true-or-false)
- [Open questions and writing areas](https://postext.dev/en/docs/exercises.md#open-questions-and-writing-areas)
- [Kana, kanji and rōmaji](https://postext.dev/en/docs/japanese-layout.md#kanji-kana-and-rōmaji)
- [Chinese, Japanese and Korean fonts](https://postext.dev/en/docs/configuration-pdf-output.md#chinese-japanese-and-korean-fonts)
- [Side lines (bōsen)](https://postext.dev/en/docs/japanese-layout.md#side-lines-bōsen)
- [Books bound on the right](https://postext.dev/en/docs/configuration-page-layout.md#binding)
- [Inline chips](https://postext.dev/en/docs/configuration-styles.md#chip-styles)
- [Three or more columns](https://postext.dev/en/docs/configuration-page-layout.md#layout-types)
- [Designed openers](https://postext.dev/en/docs/configuration-headings.md#span-and-advanced-design)
- [Heading attributes](https://postext.dev/en/docs/document-format.md#heading-attributes)
- [Pictures in page designs](https://postext.dev/en/docs/configuration-headers-footers.md#image-elements)
- [Anchoring design elements](https://postext.dev/en/docs/configuration-headers-footers.md#element-placement)
- [Semantic colour palette](https://postext.dev/en/docs/configuration-fonts-colors-viewers.md#color-palette)
- [PDF export](https://postext.dev/en/docs/configuration-pdf-output.md#generating-pdfs)
- [Columns in a box or in the text](https://postext.dev/en/docs/document-format-directives.md#columns)
- [Boxes that split or stay whole](https://postext.dev/en/docs/configuration-callouts.md#the-callout-container)
- [Chinese line breaking](https://postext.dev/en/docs/configuration-east-asian.md#east-asian-typography)
- [Column balancing](https://postext.dev/en/docs/configuration-page-flow.md#column-balancing)
- [Paragraph styles](https://postext.dev/en/docs/configuration-styles.md#paragraph-styles)
- [Fonts embedded in the PDF](https://postext.dev/en/docs/configuration-pdf-output.md#why-a-font-provider)
- [Figures and tables as resources](https://postext.dev/en/docs/document-format-resources.md#resources)

**Config at a glance**

- [`bodyText`](https://postext.dev/en/docs/configuration-text.md#body-text), [`calloutStyles`](https://postext.dev/en/docs/configuration-callouts.md#callout-styles), [`chipStyles`](https://postext.dev/en/docs/configuration-styles.md#chip-styles), [`colorPalette`](https://postext.dev/en/docs/configuration-fonts-colors-viewers.md#color-palette), `exerciseStyles`, [`footer`](https://postext.dev/en/docs/configuration-headers-footers.md#headers--footers), [`header`](https://postext.dev/en/docs/configuration-headers-footers.md#headers--footers), [`headings`](https://postext.dev/en/docs/configuration-headings.md#headings), [`layout`](https://postext.dev/en/docs/configuration-page-layout.md#layout), [`locale`](https://postext.dev/en/docs/configuration-language.md#hyphenation), [`orderedLists`](https://postext.dev/en/docs/configuration-lists-math.md#ordered-lists), [`page`](https://postext.dev/en/docs/configuration-page-layout.md#page), [`paragraphStyles`](https://postext.dev/en/docs/configuration-styles.md#paragraph-styles)

**APIs**

- [`buildDocument`](https://postext.dev/en/docs/configuration-programmatic-usage.md#building-a-document), [`decompressWoff2`](https://postext.dev/en/docs/configuration-pdf-output.md#browser-font-provider-fontsource--woff2), `loadVerticalAlternates`, [`registerResourceImage`](https://postext.dev/en/docs/architecture.md#api-surface), [`renderPageToCanvas`](https://postext.dev/en/docs/configuration-programmatic-usage.md#rendering-a-page-to-a-bitmap), [`renderToPdf`](https://postext.dev/en/docs/configuration-pdf-output.md#generating-pdfs), [`withLoadedFonts`](https://postext.dev/en/docs/configuration-programmatic-usage.md#loading-fonts-before-layout)

**Typefaces**

- Klee One (OFL-1.1), Zen Maru Gothic (OFL-1.1)

## Method

### 1 · Turn each exercise's key upside down

The code is [the short answer](https://postext.dev/en/cookbook/japanese-drill-upside-down-answers.md#the-short-answer) above. `placement: 'inverted'` sets the key after each exercise in a box turned 180°, and the box goes inside the exercise's own box, so a page break never parts the two. The key is made from the exercise: the operations with their results, the katakana of the right option, ○ and ×, the words of the gaps. The answers box style, `kotae`, only sets the type small and grey.

### 2 · One band for a page across and a page down

```js
// script.js, lines 59–76
// A heading design on a vertical page is laid along its column: x runs down the page and y
// to the left, so the same band stands at the right edge, from head to foot.
const BAND = 30; // mm: the band's depth (its height across, its width down)
const header = { enabled: true, minHeight: mm(BAND + 3), slot: { elements: [
  { kind: 'box', id: 'band', reserve: false, style: { backgroundColor: col('tint'),
    borderRadius: mm(4) }, placement: { anchor: { to: 'container', edge: 'top-left' },
    size: { width: 'fill', height: mm(BAND) } } },
  { kind: 'image', id: 'mascot', resourceId: '{attr.pic}', decorative: true, reserve: false,
    placement: { anchor: { to: 'container', edge: 'top-right' }, offset: { x: mm(-4), y: mm(1) },
      size: { width: mm(28), height: mm(28) } } },
  { kind: 'text', id: 'subject', content: '{attr.kicker}', fontFamily: ROUND, fontSize: pt(10),
    fontWeight: 700, color: col('ink'), box: { backgroundColor: col('sun'), borderRadius: mm(3),
      padding: { top: mm(0.6), bottom: mm(0.6), left: mm(2.4), right: mm(2.4) } },
    placement: { anchor: { to: 'container', edge: 'top-left' }, offset: { x: mm(5), y: mm(5) } } },
  { kind: 'text', id: 'title', content: '{titleText}', fontFamily: ROUND, fontSize: pt(20),
    fontWeight: 700, color: col('ink'),
    placement: { anchor: { to: '#subject', edge: 'below' }, offset: { x: mm(0), y: mm(2.5) } } },
] } };
```

A heading design on a vertical page is laid along its column: x runs down the page and y runs to the left. The band anchored `top-left` with the full width stands at the top of the arithmetic page and down the right edge of the kanji page; the mascot anchored `top-right` sits at the band's far end on both. Nothing in the design names a direction.

### 3 · Two drills from one text

```js
// script.js, lines 271–279
// Two drill books of one series: arithmetic across, bound on the left; kanji in columns,
// bound on the right (vertical text binds there by itself).
const [sansu, kokugo] = markdown.split(/(?=^# 春のことば)/m);
const build = (text) => withLoadedFonts(() => buildDocument({ markdown: text, resources },
  config()), { ...kitFonts(FONTS), text: markdown });
const across = await build(sansu);
// 国語 is set in columns, top to bottom, right to left: the same design, turned.
writingMode = 'vertical-rl';
const docs = [across, await build(kokugo)];
```

The configuration is a function, so each build gets its own object, and only `writingMode` changes between the two. Set vertically, the 国語 drill binds on the right by itself; `showBook` lays each drill out on its own side of the spine. The text is set in Klee One, a textbook face, and the labels in Zen Maru Gothic; both load their vertical punctuation for the brackets of the kanji page.

## The whole recipe

One file, composed from the recipe's folder with the sample text and the Cookbook's shared kit inlined; it builds its own page. To run it, put it in a `<script type="module">` on an empty page, or paste it into the JS panel of a new CodePen (as a module). It imports postext from esm.sh, so there is nothing to install or build.

- Source folder: https://github.com/drnachio/postext/tree/main/cookbook/japanese-drill-upside-down-answers

### script.js

```js
// ═══ Postext Cookbook · Nº 172 · A Japanese drill with the answers upside down ═══
// https://postext.dev/en/cookbook/japanese-drill-upside-down-answers
// Code: MIT · Text: original (CC BY 4.0) · Pictures: generated with diffusion models
// Fonts: Klee One, Zen Maru Gothic (SIL OFL 1.1) · Needs postext ≥ 1.59.0
import {
  buildDocument, withLoadedFonts, renderPageToCanvas, registerResourceImage,
  loadVerticalAlternates,
} from 'https://esm.sh/postext';
import { renderToPdf, decompressWoff2 } from 'https://esm.sh/postext-pdf';

const LANG = 'ja'; // @lang: the language of the frame; the drill is Japanese in all
const RECIPE = 'japanese-drill-upside-down-answers';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// #region palette: a drill book's blue, a warm yellow and a pale sky for the band
const palette = {
  ink: '#23272c', // text
  blue: '#2a6cb0', // the accent: exercise numbers, the title band's rule, the score box
  sun: '#f2c14e', // the subject badge
  tint: '#eaf2fb', // the title band
  rule: '#a8bfd8', // writing lines and boxes
  muted: '#69717b', // folios, the name line, the upside-down answers
  paper: '#ffffff',
};
const col = (id) => ({ hex: palette[id], model: 'hex', paletteId: id });
const colorPalette = [
  ...Object.entries(palette).map(([id, hex]) => ({ id, name: id, value: { hex, model: 'hex' } })),
  { id: 'main-color', name: 'accent (defaults)', value: { hex: palette.blue, model: 'hex' } },
];
// #endregion
// 教科書体 for the text a child copies from, a round gothic for the labels.
const [TEXT, ROUND] = ['Klee One', 'Zen Maru Gothic'];

// #region answer: the answers printed upside down under each exercise
// `placement: 'inverted'` sets each exercise's key right after it in a box turned 180°: the
// pupil sees where the answers are without reading them, and turns the book to check. The
// key's words come from the exercise (the options' katakana, ○ and ×, the operations), so
// the Markdown holds nothing twice.
const drill = {
  id: 'drill',
  number: { shape: 'square', fontFamily: TEXT, fontWeight: 600, background: col('blue') },
  instruction: { fontFamily: ROUND, bold: false },
  options: { layout: 'row' }, // ア イ ウ side by side (the default labels in Japanese)
  trueFalse: { look: 'bracket' }, // （　） for ○ or ×
  blank: { look: 'box', width: 'answer', color: col('rule') }, // □ to write in
  area: { kind: 'lines', color: col('rule') },
  grid: { rule: col('rule') },
  solutions: { placement: 'inverted', box: 'kotae' },
  marginTop: em(1.1), marginBottom: em(0.4),
};
const kotae = { id: 'kotae', title: '', backgroundEnabled: false, border: { enabled: false },
  padding: { top: pt(0), right: pt(0), bottom: pt(0), left: pt(0) },
  body: { fontFamily: ROUND, fontSize: pt(8), lineHeight: pt(12), color: col('muted'),
    firstLineIndent: pt(0) },
  marginTop: mm(1), marginBottom: mm(2), keepTogether: true };
// #endregion

// #region header: the drill's band: subject badge, title, the mascot at the far end
// A heading design on a vertical page is laid along its column: x runs down the page and y
// to the left, so the same band stands at the right edge, from head to foot.
const BAND = 30; // mm: the band's depth (its height across, its width down)
const header = { enabled: true, minHeight: mm(BAND + 3), slot: { elements: [
  { kind: 'box', id: 'band', reserve: false, style: { backgroundColor: col('tint'),
    borderRadius: mm(4) }, placement: { anchor: { to: 'container', edge: 'top-left' },
    size: { width: 'fill', height: mm(BAND) } } },
  { kind: 'image', id: 'mascot', resourceId: '{attr.pic}', decorative: true, reserve: false,
    placement: { anchor: { to: 'container', edge: 'top-right' }, offset: { x: mm(-4), y: mm(1) },
      size: { width: mm(28), height: mm(28) } } },
  { kind: 'text', id: 'subject', content: '{attr.kicker}', fontFamily: ROUND, fontSize: pt(10),
    fontWeight: 700, color: col('ink'), box: { backgroundColor: col('sun'), borderRadius: mm(3),
      padding: { top: mm(0.6), bottom: mm(0.6), left: mm(2.4), right: mm(2.4) } },
    placement: { anchor: { to: 'container', edge: 'top-left' }, offset: { x: mm(5), y: mm(5) } } },
  { kind: 'text', id: 'title', content: '{titleText}', fontFamily: ROUND, fontSize: pt(20),
    fontWeight: 700, color: col('ink'),
    placement: { anchor: { to: '#subject', edge: 'below' }, offset: { x: mm(0), y: mm(2.5) } } },
] } };
// #endregion

let writingMode = 'horizontal-tb'; // 算数 runs across the page
const config = () => ({
  locale: 'ja',
  colorPalette,
  page: { sizePreset: 'custom', width: mm(182), height: mm(257), dpi: 150, // B5
    margins: { top: mm(18), bottom: mm(16), left: mm(16), right: mm(16), mirror: true } },
  layout: { layoutType: 'single', writingMode },
  bodyText: { fontFamily: TEXT, fontSize: pt(12), lineHeight: pt(22), color: col('ink'),
    boldColor: col('ink'), italicColor: col('ink'), referenceColor: col('ink'),
    boldFontWeight: 600, // Klee One's heaviest cut
    textAlign: 'left', firstLineIndent: pt(0) },
  headings: { fontFamily: ROUND, color: col('ink'), fontWeight: 700, balancing: { enabled: false },
    levels: [{ level: 1, fontSize: pt(20), breakBefore: { parity: 'any' }, marginBottom: pt(0),
      advancedDesign: header }] },
  orderedLists: { numberFormat: 'arabic', color: col('ink'), fontWeight: 600 },
  paragraphStyles: [
    { id: 'namae', fontFamily: ROUND, fontSize: pt(10), color: col('muted'), textAlign: 'right',
      firstLineIndent: pt(0), marginTop: pt(0), marginBottom: mm(1) },
    { id: 'colophon', fontFamily: ROUND, fontSize: pt(7.5), lineHeight: pt(11), color: col('muted'),
      textAlign: 'left', firstLineIndent: pt(0), marginTop: mm(5) },
  ],
  chipStyles: [{ id: 'sen', backgroundEnabled: false, underline: 'solid', borderWidth: pt(0.7),
    borderColor: col('muted'), minWidth: mm(40), paddingX: pt(0), paddingY: pt(0) },
  { id: 'waku', backgroundEnabled: false, borderWidth: pt(1), borderColor: col('blue'),
    borderRadius: mm(1.5), minWidth: mm(16), paddingY: em(0.2) }],
  calloutStyles: [kotae],
  exerciseStyles: [drill],
  header: { elements: [] },
  footer: { elements: [{ kind: 'text', id: 'folio', content: '{pageNumber}', fontFamily: ROUND,
    fontSize: pt(9), fontWeight: 700, color: col('blue'), align: 'center',
    placement: { anchor: { to: 'page', edge: 'bottom' }, offset: { x: mm(0), y: mm(-9) } } }] },
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`---
title: "3年生のまいにちドリル"
---

# 3けたのたし算とひき算 {kicker="さんすう　12" pic="tanuki"}

:::paragraphs{style="namae"}
名前:chip[　]{style="sen"}　　:chip[　]{style="waku"}点
:::

:::exercise{type=arithmetic}
ひっ算でしましょう。（1つ5点）

- 345 + 278
- 902 - 456
- 124 × 3
- 864 ÷ 4
:::

:::exercise
□にあてはまる数を書きましょう。（1つ5点）

:::columns{count=2}
25 + 37 = [[62]]

90 − 46 = [[44]]

8 × 7 = [[56]]

400 + 600 = [[1000]]

1000 − 1 = [[999]]

63 ÷ 9 = [[7]]
:::
:::

:::exercise{columns=3}
正しいものをえらんで、記号で答えましょう。（1つ5点）

1. 1000は、100を何こ集めた数ですか。
   - [ ] 1こ
   - [x] 10こ
   - [ ] 100こ
2. 500円玉を2まい出すと、何円ですか。
   - [ ] 700円
   - [ ] 520円
   - [x] 1000円
:::

:::exercise{type=truefalse}
正しいものには○、まちがっているものには×を書きましょう。（1つ5点）

- [x] 345 + 278 の答えは、600より大きい。
- [ ] 902 − 456 の答えは、500より大きい。
- [x] 124 × 3 と 3 × 124 は、同じ答えになる。
:::

:::exercise{type=open area=lines lines=2}
354円のノートと278円のペンを買いました。あわせて何円ですか。（式5点・答え5点）

:::solution
式　354 + 278 = 632　　答え　632円
:::
:::

:::exercise{type=open area=lines lines=2}
456ページの本を、きのうまでに278ページ読みました。のこりは何ページですか。（式5点・答え5点）

:::solution
式　456 − 278 = 178　　答え　178ページ
:::
:::

# 春のことば {kicker="こくご　12" pic="kitsune"}

:::paragraphs{style="namae"}
名前:chip[　]{style="sen"}　　:chip[　]{style="waku"}点
:::

:::exercise
□に漢字を書きましょう。（1つ5点）

:::columns{count=3}
はる

[[春]]

はな

[[花]]

かぜ

[[風]]

そら

[[空]]

あさ

[[朝]]

ひる

[[昼]]
:::
:::

:::exercise
線を引いた漢字の読みがなを書きましょう。（1つ5点）

1. :sideline[春風]がふく。（[[はるかぜ]]）
2. :sideline[朝日]がのぼる。（[[あさひ]]）
3. 花の:sideline[色]がきれいだ。（[[いろ]]）
:::

:::exercise
文に合うことばを、○でかこみましょう。（1つ5点）

1. 春の風がふいて、さくらの花が [[(ちりました) | のぼりました]]。
2. 朝、つばめが南の国から [[(やってきた) | ねむっていた]]。
:::

:::exercise{columns=1}
ことばのいみに合うものを、えらびましょう。（10点）

「うららか」とは、どんなようすですか。

- [ ] 雨がはげしくふるようす
- [x] 空が晴れて、日の光がやわらかいようす
- [ ] 風がつめたくふくようす
:::

:::paragraphs{style="colophon"}
書体：Klee One、Zen Maru Gothic（SIL OFL）　絵：拡散モデルで生成　問題：本書のための書き下ろし（CC BY 4.0）
:::
`; // content.ja.md: the さんすう page, then the こくご page

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
const FONTS = {
  'Klee One': ['400', '600'], // 教科書体: the text and the numbers to copy
  'Zen Maru Gothic': ['400', '700'], // labels, instructions, titles, the answers
};

// ─── 4 · Build & show ───────────────────────────────────────────────────────
// Each face loads the files of the characters it sets (gotcha: cjk-fonts-slices); the
// vertical page also needs each face's upright punctuation.
await loadFonts(FONTS, markdown);
await loadCjkFonts(FONTS, markdown, { vertical: true });
const resources = [];
for (const id of ['tanuki', 'kitsune']) {
  await loadImage(`${id}-600.jpg`, asset(id === 'tanuki' ? 'tanuki-600.jpg' : 'kitsune-600.jpg'));
  resources.push({ id, typeId: 'figure', kind: 'bitmap', createdAt: 0, updatedAt: 0,
    bitmap: { fileId: `${id}-600.jpg`, format: 'jpeg', width: 600, height: 600 } });
}
// #region two-books: one drill across, one in columns, with the same styles
// Two drill books of one series: arithmetic across, bound on the left; kanji in columns,
// bound on the right (vertical text binds there by itself).
const [sansu, kokugo] = markdown.split(/(?=^# 春のことば)/m);
const build = (text) => withLoadedFonts(() => buildDocument({ markdown: text, resources },
  config()), { ...kitFonts(FONTS), text: markdown });
const across = await build(sansu);
// 国語 is set in columns, top to bottom, right to left: the same design, turned.
writingMode = 'vertical-rl';
const docs = [across, await build(kokugo)];
// #endregion
showBook(docs, { title: t({ ja: '答えがさかさまのドリル', en: 'A Japanese drill, answers upside down',
  es: 'Un cuaderno japonés con las soluciones del revés' }) });
offerPdf(() => renderToPdf(docs, { fontProvider: cjkPdfProvider, resourceBytes: imageBytes }),
  `${RECIPE}.pdf`);

// ─── Kit ── helpers shared by every Cookbook recipe · postext.dev/cookbook ─────

// ─── Kit · core v1 ── the same in every recipe · postext.dev/cookbook
function mm(value) { return { value, unit: 'mm' }; }
function pt(value) { return { value, unit: 'pt' }; }
function em(value) { return { value, unit: 'em' }; }
/** The sample language's string: t({ en: 'Figure', es: 'Figura' }). */
function t(strings) { return strings[LANG] ?? Object.values(strings)[0]; }
/** A file in this recipe's assets folder, served from the Postext repo by jsDelivr. */
function asset(file) { return `https://cdn.jsdelivr.net/gh/drnachio/postext@main/cookbook/${RECIPE}/assets/${file}`; }

// ─── Kit · fonts v3 ── the same in every recipe · postext.dev/cookbook
// Postext loads the faces a config asks for before layout and asks the kit
// for Fontsource's files, the ones the PDF embeds too.

/** buildDocumentWithFonts' options: the resolver, and FONTS' faces loaded
 *  with the config's. FONTS = { 'Family Name': ['400', '400i', '700'] }. */
function kitFonts(FONTS = {}) {
  const faces = Object.entries(FONTS).flatMap(([family, specs]) => specs.map((spec) =>
    ({ family, weight: parseInt(spec, 10), style: spec.endsWith('i') ? 'italic' : 'normal' })));
  return { resolve: fontsourceResolver, faces };
}

/** A face's files with their ranges: latin, then latin-ext and greek when
 *  `text` needs them (kitSubsetsFor). Null for a face Fontsource lacks. */
async function fontsourceResolver(family, weight, style, { text = '' } = {}) {
  const id = fontsourceId(family);
  const meta = await fontsourceMeta(family);
  if (meta && !(await fontsourceWeights(family, style)).includes(weight)) return null;
  kitStatus('Loading fonts…');
  const at = await fontsourceAt(id);
  return ['latin', ...kitSubsetsFor(text, meta)].map((subset) => ({
    source: `${at}files/${id}-${subset}-${weight}-${style}.woff2`,
    unicodeRange: kitRanges()[subset],
  }));
}

/** Each file's unicode-range (a function: the kit runs after the pen's code). */
function kitRanges() {
  return {
    latin: 'U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,'
      + 'U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD',
    'latin-ext': 'U+0100-02BA,U+02BD-02C5,U+02C7-02CC,U+02CE-02D7,U+02DD-02FF,U+0304,U+0308,U+0329,'
      + 'U+1D00-1DBF,U+1E00-1E9F,U+1EF2-1EFF,U+2020,U+20A0-20AB,U+20AD-20C0,U+2113,U+2C60-2C7F,U+A720-A7FF',
    greek: 'U+0370-03FF',
  };
}

/** For the cjk, arabic and comics blocks: loads `faces` (as FONTS) for the
 *  sample `text`; `optional` skips a face Fontsource lacks. Files are added in
 *  the order asked, the last winning a shared character. Resolves to the count. */
async function loadFonts(faces, text = '', { optional = false } = {}) {
  kitStatus('Loading fonts…');
  const ranges = kitRanges();
  const jobs = [];
  for (const [family, specs] of Object.entries(faces)) {
    const id = fontsourceId(family);
    const todo = [...new Set(specs)].map((spec) => [parseInt(spec, 10), spec.endsWith('i') ? 'italic' : 'normal'])
      .filter(([weight, style]) => !hasFace(family, weight, style)); // before any await
    const at = fontsourceAt(id);
    const meta = optional || /[^\0-ÿ]/u.test(text) ? await fontsourceMeta(family) : null;
    const subsets = ['latin', ...kitSubsetsFor(text, meta)];
    for (const [weight, style] of todo) {
      if (optional && !(meta && (await fontsourceWeights(family, style)).includes(weight))) continue;
      for (const subset of subsets) {
        const url = `${await at}files/${id}-${subset}-${weight}-${style}.woff2`;
        const face = new FontFace(family, `url(${url}) format('woff2')`,
          { weight: String(weight), style, unicodeRange: ranges[subset] });
        jobs.push(face.load().catch(() => {
          if (subset === 'latin' && !optional) throw new Error(`Fontsource has no ${family} ${weight} ${style}`);
        }));
      }
    }
  }
  const ready = await Promise.all(jobs).catch((error) => { kitFail(error); throw error; });
  return ready.filter((face) => face && document.fonts.add(face)).length;
}

/** A loaded FontFace covers this face (fonts.check() says yes to any family). */
function hasFace(family, weight, style) {
  for (const face of document.fonts) {
    if (face.status !== 'loaded' || face.style !== style) continue;
    if (face.family.replace(/^["']|["']$/g, '') !== family) continue;
    const [low, high = low] = face.weight.split(' ').map(Number);
    if (weight >= low && weight <= high) return true;
  }
  return false;
}

/** The files beyond latin `text` needs that `meta`'s family ships. */
function kitSubsetsFor(text, meta) {
  return [[/[Ā-˿ᴀ-ᶿḀ-ỿ†ℓⱠ-Ɀ꜠-ꟿ]/u, 'latin-ext'], [/[Ͱ-Ͽ]/u, 'greek']]
    .filter(([re, x]) => re.test(text) && meta?.subsets?.includes(x)).map(([, x]) => x);
}

/** Fontsource's id for a family: 'Source Serif 4' → 'source-serif-4'. */
function fontsourceId(family) { return family.toLowerCase().replace(/\s+/g, '-'); }

/** A package's folder at the one version @5 names now (#766). */
function fontsourceAt(id, u = `https://cdn.jsdelivr.net/npm/@fontsource/${id}@`) {
  return (fontsourceAt.c ??= {})[id] ??= fetch(u + '5/package.json').then((r) => r.json())
    .then((p) => p.version || 5, () => 5).then((v) => `${u}${v}/`);
}

/** The family's Fontsource metadata (weights, styles, subsets), or null. */
function fontsourceMeta(family, id = fontsourceId(family)) {
  return (fontsourceMeta.c ??= {})[id] ??= fetch(`https://api.fontsource.org/v1/fonts/${id}`)
    .then((res) => (res.ok ? res.json() : null), () => null);
}

/** The weights the package ships in `style`: the API pairs none (no Libre
 *  Caslon 700 italic file), so italics are read from latin-italic.css. */
function fontsourceWeights(family, style, id = fontsourceId(family)) {
  return (fontsourceWeights.c ??= {})[id + style] ??= fontsourceMeta(family).then(async (m) => {
    if (!m?.styles.includes(style)) return m ? [] : [400, 700];
    const css = style === 'italic' ? await fetch(`${await fontsourceAt(id)}latin-italic.css`).then((r) => (r.ok ? r.text() : ''), () => '') : '';
    const w = [...css.matchAll(/weight: (\d+)/g)].map((x) => +x[1]);
    return w.length ? w : m.weights;
  });
}

// ─── Kit · viewer v2 ── the same in every recipe · postext.dev/cookbook
/** The pages as spreads on a dark desk, page 1 alone, then verso | recto,
 *  each painted when it scrolls near. Other options go to renderPageToCanvas. */
function showPages(docs, { title, width = 460, ...render } = {}) {
  const root = viewer(title);
  const pages = [docs].flat().flatMap((doc) =>
    doc.pages.map((page) => ({ doc, page, n: (doc.pageIndexOffset ?? 0) + page.index })));
  const spreads = [];
  let verso = null;
  for (const p of pages) {
    if (p.n % 2 === 1) { if (verso) spreads.push([verso, null]); verso = p; }
    else { spreads.push([verso, p]); verso = null; }
  }
  if (verso) spreads.push([verso, null]);
  const density = Math.min(window.devicePixelRatio || 1, 2);
  showPages.painter?.disconnect();
  const painter = new IntersectionObserver((entries) => {
    for (const { isIntersecting, target } of entries) {
      if (!isIntersecting) continue;
      painter.unobserve(target);
      const { doc, page } = target.postext;
      renderPageToCanvas(page, doc, target, { ...render, scale: (width * density) / page.width });
    }
  }, { rootMargin: '800px' });
  showPages.painter = painter;
  root.replaceChildren(...spreads.map((pair) => {
    const spread = document.createElement('div');
    spread.className = 'pt-spread';
    for (const p of pair) {
      const figure = document.createElement('figure');
      if (p) {
        const label = p.page.pageLabel || String(p.n + 1);
        const canvas = document.createElement('canvas');
        canvas.postext = p;
        canvas.style.aspectRatio = `${p.page.width} / ${p.page.height}`;
        canvas.setAttribute('role', 'img');
        canvas.setAttribute('aria-label', `Page ${label}`);
        const folio = document.createElement('figcaption');
        folio.textContent = label;
        figure.append(canvas, folio);
        painter.observe(canvas);
      } else figure.className = 'pt-blank';
      spread.append(figure);
    }
    return spread;
  }));
  kitStatus(`${pages.length} ${pages.length === 1 ? 'page' : 'pages'}`);
  document.documentElement.dataset.postext = 'ready';
  return pages.length;
}

/** The desk, the bar and the error reporting, created once. */
function viewer(title) {
  if (!document.getElementById('pt-kit')) {
    document.head.insertAdjacentHTML('beforeend', `<style id="pt-kit">
      :root { color-scheme: dark; }
      body { margin: 0; background: #0e1014; color: #b9bcc4; font: 13px/1.45 system-ui, sans-serif; }
      #pt-bar { position: sticky; top: 0; z-index: 1; display: flex; flex-wrap: wrap; align-items: center;
        gap: 6px 16px; padding: 10px 16px; background: rgb(14 16 20 / .92); backdrop-filter: blur(6px);
        border-bottom: 1px solid #23262d; }
      #pt-bar strong { color: #f4f1ea; font-weight: 600; }
      #pt-actions { display: flex; gap: 12px; margin-left: auto; }
      #pt-actions a, #pt-actions button { color: #d8a21a; font: inherit; background: none; border: 0; padding: 0; cursor: pointer; }
      #pages { display: grid; justify-items: center; gap: 48px; padding: 32px 16px 72px; }
      .pt-spread { display: flex; }
      .pt-spread figure { margin: 0; width: min(460px, 44vw); }
      .pt-spread canvas { display: block; width: 100%; background: #fff;
        box-shadow: 0 1px 2px rgb(0 0 0 / .5), 0 22px 44px -16px rgb(0 0 0 / .8); }
      .pt-spread figure:first-child canvas { box-shadow: inset -14px 0 14px -14px rgb(0 0 0 / .18), 0 1px 2px rgb(0 0 0 / .5), 0 22px 44px -16px rgb(0 0 0 / .8); }
      .pt-spread figcaption { margin-top: 10px; text-align: center; font: 600 10px/1 system-ui, sans-serif;
        letter-spacing: .18em; text-transform: uppercase; color: #6c7079; }
      .pt-blank { visibility: hidden; }
      @media (max-width: 760px) {
        .pt-spread { flex-direction: column; gap: 32px; }
        .pt-spread figure { width: min(460px, 92vw); }
        .pt-blank { display: none; }
      }
    </style>`);
    document.body.insertAdjacentHTML('afterbegin',
      '<header id="pt-bar"><strong id="pt-title"></strong><span id="pt-status" role="status"></span><span id="pt-actions"></span></header>');
    document.getElementById('pt-title').textContent = document.title || 'Postext';
    addEventListener('error', (event) => kitFail(event.error ?? event.message));
    addEventListener('unhandledrejection', (event) => kitFail(event.reason));
  }
  if (title) document.getElementById('pt-title').textContent = title;
  return document.getElementById('pages')
    ?? document.body.appendChild(Object.assign(document.createElement('main'), { id: 'pages' }));
}

function kitStatus(text) {
  viewer();
  document.getElementById('pt-status').textContent = text;
}

function kitFail(error) {
  document.documentElement.dataset.postext = 'error';
  kitStatus(`Error: ${error?.message ?? error}`);
}

// ─── Kit · pdf v3 ── the same in every recipe that exports a PDF
/** The Fontsource files the screen used, as TrueType, with their range and
 *  place: the nearest weight the family ships in that style, upright with no italic;
 *  latin, then what its letters need (kitSubsetsFor). */
async function fontsourceProvider(family, weight, style, request) {
  const id = fontsourceId(family);
  const meta = await fontsourceMeta(family);
  const s = style === 'italic' && meta && !meta.styles.includes('italic') ? 'normal' : style;
  const shipped = meta ? await fontsourceWeights(family, s) : [];
  const weights = shipped.length ? shipped : [400, 700];
  const w = weights.reduce((a, b) => (Math.abs(b - weight) < Math.abs(a - weight) ? b : a));
  const text = String.fromCodePoint(...(request?.codePoints ?? []));
  const files = await Promise.all(['latin', ...kitSubsetsFor(text, meta)].map(async (subset, order) => {
    const res = await fetch(`${await fontsourceAt(id)}files/${id}-${subset}-${w}-${s}.woff2`);
    if (!res.ok) throw new Error(`Fontsource has no ${family} ${w} ${s} ${subset}`);
    return Object.assign(await decompressWoff2(new Uint8Array(await res.arrayBuffer())),
      { unicodeRange: kitRanges()[subset], order });
  }));
  return files.length === 1 ? files[0] : files;
}

/** A "Build the PDF" button; then "Open the PDF" (a new tab: CodePen's frame
 *  shows no PDFs) and a download link. */
function offerPdf(makePdf, filename) {
  viewer();
  const button = Object.assign(document.createElement('button'), { type: 'button', textContent: 'Build the PDF' });
  button.dataset.postextPdf = filename;
  button.addEventListener('click', async () => {
    button.disabled = true;
    button.textContent = 'Building the PDF…';
    try {
      const bytes = await makePdf();
      const url = URL.createObjectURL(new Blob([bytes], { type: 'application/pdf' }));
      const size = `${Math.max(1, Math.round(bytes.length / 1024))} KB`;
      button.replaceWith(
        Object.assign(document.createElement('a'), { href: url, target: '_blank', rel: 'noopener', textContent: 'Open the PDF ↗' }),
        Object.assign(document.createElement('a'), { href: url, download: filename, textContent: `Download ${filename} · ${size}` }));
    } catch (error) {
      button.disabled = false;
      button.textContent = 'Build the PDF';
      kitFail(error);
    }
  });
  document.getElementById('pt-actions').append(button);
}

// ─── Kit · images v3 ── recipes with pictures · postext.dev/cookbook
/** Registers a photo or PNG for the canvas and keeps its bytes for the PDF.
 *  fetch → ImageBitmap never taints the canvas (a plain cross-origin <img> would). */
async function loadImage(fileId, url) {
  const res = await fetch(url);
  if (!res.ok) throw new Error(`Image not found (${res.status}): ${url}`);
  const bytes = new Uint8Array(await res.arrayBuffer());
  registerResourceImage(fileId, await createImageBitmap(new Blob([bytes])));
  (loadImage.bytes ??= new Map()).set(fileId, bytes);
}

/** Registers SVG markup as a vector image, its fonts inside (inlineSvgFonts, ≥ 1.25).
 *  `options` go to registerResourceImage: { singleInk: true } tints it on the canvas. */
async function loadSvg(fileId, svg, options) {
  if (typeof inlineSvgFonts === 'function') svg = await inlineSvgFonts(svg, svgFaces);
  const img = new Image();
  img.src = `data:image/svg+xml;charset=utf-8,${encodeURIComponent(svg)}`;
  await img.decode();
  registerResourceImage(fileId, img, options);
  (loadImage.bytes ??= new Map()).set(fileId, new TextEncoder().encode(svg));
}

/** A face's Fontsource files: nearest weight; latin + what the SVG sets. */
async function svgFaces(family, weight, style, { codePoints = [] } = {}) {
  const [id, m] = [fontsourceId(family), await fontsourceMeta(family)];
  const w = m?.weights.reduce((a, b) => (Math.abs(b - weight) < Math.abs(a - weight) ? b : a)) ?? weight;
  const s = m?.styles.includes(style) === false ? 'normal' : style;
  return Promise.all(['latin', ...kitSubsetsFor(String.fromCodePoint(...codePoints), m)].map(async (x) => new Uint8Array(
    await (await fetch(`${await fontsourceAt(id)}files/${id}-${x}-${w}-${s}.woff2`)).arrayBuffer())));
}

/** renderToPdf({ resourceBytes: imageBytes }) */
function imageBytes(fileId) { return loadImage.bytes?.get(fileId); }

/** renderToHtml({ resourceImageUrl: imageUrl }) */
function imageUrl(fileId) {
  const bytes = imageBytes(fileId);
  if (!bytes) return undefined;
  imageUrl.urls ??= new Map();
  if (!imageUrl.urls.has(fileId)) {
    const type = /\.svg$/i.test(fileId) ? 'image/svg+xml' : /\.png$/i.test(fileId) ? 'image/png' : 'image/jpeg';
    imageUrl.urls.set(fileId, URL.createObjectURL(new Blob([bytes], { type })));
  }
  return imageUrl.urls.get(fileId);
}

// ─── Kit · cjk v2 ── Chinese, Japanese and Korean books · postext.dev/cookbook
// Fontsource ships a CJK family as about a hundred files per weight, each
// declared in its stylesheet with the unicode-range it covers. The screen
// loads the files the sample touches; the PDF gets the same files for the
// characters its pages set in each face, and embeds each as a subset.
// A book bound on the right (vertical text) is shown with its spreads
// mirrored: page 1 alone on the left of the spine, then [3 | 2].

/** The files of a Fontsource face, read from its stylesheet: { url, range,
 *  ranges }, the last declared first (the order the browser tries them in). */
function cjkSlices(family, weight, style) {
  cjkSlices.cache ??= new Map();
  const id = fontsourceId(family);
  const css = `${id}/${weight}${style === 'italic' ? '-italic' : ''}.css`;
  if (!cjkSlices.cache.has(css)) {
    let at;
    cjkSlices.cache.set(css, fontsourceAt(id).then((a) => fetch(at = a + css.slice(id.length + 1)))
      .then((res) => {
        if (!res.ok) throw new Error(`Fontsource has no ${family} ${weight} ${style} (${res.status})`);
        return res.text();
      })
      .then((text) => [...text.matchAll(/@font-face\s*{([^}]*)}/g)].map(([, rule]) => {
        const range = /unicode-range:\s*([^;]+);/.exec(rule)?.[1].trim() ?? 'U+0-10FFFF';
        const ranges = range.split(',').map((part) => {
          const [lo, hi = lo] = part.trim().slice(2).split('-');
          return [parseInt(lo, 16), parseInt(hi, 16)];
        });
        return { url: new URL(/url\(([^)]+?\.woff2)\)/.exec(rule)[1], at).href, range, ranges };
      }).reverse()));
  }
  return cjkSlices.cache.get(css);
}

/** The file of `slices` the screen sets code point `cp` in, if any: the
 *  last one loadCjkFonts adds whose range holds it. A numbered file that
 *  repeats a letter of latin is added after latin, and wins it. */
function cjkSliceFor(slices, cp) {
  const holds = (slice) => slice.ranges.some(([lo, hi]) => cp >= lo && cp <= hi);
  return slices.reduce((last, slice) => (holds(slice) ? slice : last), undefined);
}

/** Whether Fontsource serves `family` as a Chinese, Japanese or Korean
 *  family (its subsets name the script). Fails when the API does not
 *  answer: a CJK face taken for a Latin one would paint in a system face. */
async function isCjkFamily(family) {
  const meta = await fontsourceMeta(family);
  if (!meta) throw new Error(`api.fontsource.org did not describe ${family}: reload to try again`);
  return !!meta.subsets?.some((subset) => /^(chinese|japanese|korean)/.test(subset));
}

/** faces = { 'Noto Serif TC': ['400', '700'] }, as for loadFonts: the
 *  whole FONTS object may be passed, its other families are left to
 *  loadFonts. Adds one FontFace per file of each CJK face with its
 *  unicodeRange, then loads the files `text` touches. `text` is what the
 *  faces set: the sample for the text face; a book in several voices calls
 *  it once per voice (loadCjkFonts({ 'LXGW WenKai TC': ['400'] }, quotes)),
 *  so the heading and quotation faces fetch and check only their own
 *  characters. Fails when a character of `text` is in no file of a face.
 *  List every weight the pages use: a weight left to the engine's later round
 *  gets the latin file only. With { vertical: true } it also loads each
 *  family's vertical forms (brackets, quotes, pause marks) for the canvas,
 *  which needs loadVerticalAlternates imported from postext. Resolves to
 *  the number of files loaded. */
async function loadCjkFonts(faces, text, { vertical = false } = {}) {
  kitStatus('Loading fonts…');
  let loaded = 0;
  try {
    if (vertical && typeof loadVerticalAlternates !== 'function') {
      throw new Error('loadCjkFonts(…, { vertical: true }) needs loadVerticalAlternates imported from postext');
    }
    for (const [family, specs] of Object.entries(faces)) {
      if (!(await isCjkFamily(family))) continue;
      const twin = [];
      for (const spec of new Set(specs)) {
        const weight = parseInt(spec, 10);
        const style = spec.endsWith('i') ? 'italic' : 'normal';
        const slices = await cjkSlices(family, weight, style);
        const missing = [...new Set(text)].filter((ch) => /\S/.test(ch) && !cjkSliceFor(slices, ch.codePointAt(0)));
        if (missing.length) {
          throw new Error(`${family} ${spec} has no file for ${missing.slice(0, 12).join(' ')}: `
            + `give each face the text it sets (loadCjkFonts({ '${family}': ['${spec}'] }, text))`);
        }
        for (const slice of slices) {
          document.fonts.add(new FontFace(family, `url(${slice.url}) format('woff2')`,
            { weight: String(weight), style, unicodeRange: slice.range }));
          twin.push({ source: slice.url, weight: String(weight), style, unicodeRange: slice.range });
        }
        const font = `${style === 'italic' ? 'italic ' : ''}${weight} 16px "${family}"`;
        loaded += (await document.fonts.load(font, text)).length;
        if (!document.fonts.check(font, text)) throw new Error(`${family} ${spec} did not load for the sample`);
      }
      // The same files under a twin name with the `vert` feature on: the
      // canvas paints the punctuation of vertical lines with it.
      if (vertical && twin.length) await loadVerticalAlternates(family, twin);
    }
  } catch (error) {
    kitFail(error);
    throw error;
  }
  return loaded;
}

/** The PDF font provider for recipes with CJK faces: a family whose
 *  Fontsource subsets are Chinese, Japanese or Korean gets the files the
 *  screen set its pages' characters in (`request.codePoints`), each marked
 *  with its unicode-range and its place in the order loadCjkFonts added
 *  them: postext-pdf sets a character two files hold in the one added
 *  last, as the browser does. Any other family gets the latin file
 *  fontsourceProvider fetches (the "pdf" block) and, when the face sets
 *  letters only latin-ext has, that file too. */
async function cjkPdfProvider(family, weight, style, request) {
  if (!(await isCjkFamily(family))) return cjkLatinPdfFiles(family, weight, style, request);
  const meta = await fontsourceMeta(family);
  const weights = meta.weights?.length ? meta.weights : [400, 700];
  const w = weights.reduce((a, b) => (Math.abs(b - weight) < Math.abs(a - weight) ? b : a));
  const s = style === 'italic' && !meta.styles.includes('italic') ? 'normal' : style;
  const slices = await cjkSlices(family, w, s);
  const picked = new Set();
  for (const cp of request?.codePoints ?? []) {
    const slice = cjkSliceFor(slices, cp);
    if (slice) picked.add(slice);
  }
  if (!picked.size) picked.add(slices[0]);
  return Promise.all(slices.map(async (slice, order) => {
    if (!picked.has(slice)) return null;
    const res = await fetch(slice.url);
    if (!res.ok) throw new Error(`Fontsource file ${slice.url} (${res.status})`);
    const bytes = await decompressWoff2(new Uint8Array(await res.arrayBuffer()));
    return Object.assign(bytes, { unicodeRange: slice.range, order });
  })).then((files) => files.filter(Boolean));
}

/** A Latin family set next to the CJK faces: its latin file, then its
 *  latin-ext file when the face sets letters only latin-ext has (ō ū in
 *  Hepburn rōmaji, ǎ in pinyin), the file loadFonts adds on screen for
 *  them, each marked with its unicode-range and its place in that order:
 *  the PDF sets a character in the file the browser took it from. A face
 *  Fontsource ships without latin-ext, or whose file does not come, gets
 *  latin alone, and the PDF names the letters it lacks. */
async function cjkLatinPdfFiles(family, weight, style, request) {
  const meta = await fontsourceMeta(family);
  const beyond = [...(request?.codePoints ?? [])].some(cjkLatinExtOnly);
  if (!beyond || !meta?.subsets?.includes('latin-ext')) return fontsourceProvider(family, weight, style);
  const weights = meta.weights?.length ? meta.weights : [400, 700];
  const w = weights.reduce((a, b) => (Math.abs(b - weight) < Math.abs(a - weight) ? b : a));
  const s = style === 'italic' && !meta.styles.includes('italic') ? 'normal' : style;
  const id = fontsourceId(family);
  const url = `${await fontsourceAt(id)}files/${id}-latin-ext-${w}-${s}.woff2`;
  const [latin, ext] = await Promise.all([fontsourceProvider(family, weight, style), fetch(url)
    .then(async (res) => (res.ok ? decompressWoff2(new Uint8Array(await res.arrayBuffer())) : null), () => null)]);
  const ranges = kitRanges();
  return ext ? [Object.assign(latin, { unicodeRange: ranges.latin, order: 0 }),
    Object.assign(ext, { unicodeRange: ranges['latin-ext'], order: 1 })] : latin;
}

/** Whether code point `cp` is in Fontsource's latin-ext file and not in
 *  its latin file: Latin Extended-A and -B, IPA, the spacing modifiers and
 *  Latin Extended Additional (loadFonts's test for latin-ext), less the
 *  few latin holds too (ı Œ œ ʻ ʼ ˆ ˚ ˜). */
function cjkLatinExtOnly(cp) {
  if (!((cp >= 0x100 && cp <= 0x2ff) || (cp >= 0x1e00 && cp <= 0x1eff))) return false;
  return ![0x131, 0x152, 0x153, 0x2bb, 0x2bc, 0x2c6, 0x2da, 0x2dc].includes(cp);
}

/** showPages for a book bound on either edge. A right-bound book (the
 *  document says so: doc.binding is 'right' for page.binding 'right' and
 *  for vertical text) lies on the desk as it opens: page 1 alone on the
 *  left of the spine, then [3 | 2], the spine shade on each page's inner
 *  edge. `binding` ('left' | 'right') overrides the document's. */
function showBook(docs, { binding, ...options } = {}) {
  const count = showPages(docs, options);
  const right = (binding ?? [docs].flat()[0]?.binding) === 'right';
  if (!document.getElementById('pt-kit-cjk')) {
    // The pages keep direction ltr: a canvas draws text in the direction its
    // element inherits, and under rtl each run would end where the engine
    // starts it, its brackets mirrored.
    document.head.insertAdjacentHTML('beforeend', `<style id="pt-kit-cjk">
      .pt-spread[dir="rtl"] canvas { direction: ltr; }
      .pt-spread[dir="rtl"] figure:first-child canvas { box-shadow: inset 14px 0 14px -14px rgb(0 0 0 / .18),
        0 1px 2px rgb(0 0 0 / .5), 0 22px 44px -16px rgb(0 0 0 / .8); }
    </style>`);
  }
  // Each pair stays [verso, recto] in the page; right to left, the verso
  // sits on the right. Phones stack the pages in reading order either way.
  for (const spread of document.querySelectorAll('#pages > .pt-spread')) spread.dir = right ? 'rtl' : 'ltr';
  document.getElementById('pages').dataset.binding = right ? 'right' : 'left';
  return count;
}

// ─── /Kit ───────────────────────────────────────────────────────────────────────
```

## Variations

### Collect the answers at the end

A drill printed with a separate answer booklet keeps the key out of the pages: `chapterEnd` lists it after the last exercise.

```diff
-  solutions: { placement: 'inverted', box: 'kotae' },
+  solutions: { placement: 'chapterEnd', box: 'kotae' },
```

### Print a puzzle page

[The puzzle page](https://postext.dev/en/cookbook/puzzle-page-upside-down-answers.md) turns its answers the same way, on cards in two columns.

## Pitfalls

- **Chinese faces load by slices, through the cjk block.** Fontsource serves a Chinese, Japanese or Korean family as about a hundred files per weight, each covering a range of characters. loadFonts fetches only the latin file, so on screen the Han characters come from a system face and measure wrong, and fontsourceProvider hands the PDF that latin file, which prints them as empty boxes. List the cjk kit block, call loadCjkFonts(FONTS, markdown) after loadFonts (once per voice, with the text it sets, when the book uses several CJK faces) and give renderToPdf fontProvider: cjkPdfProvider: both take the files that hold the text's characters.
- **Tag a Japanese text 'ja', never zh-Hans or LANG.** A recipe's editions are en and es, but a Japanese sample is Japanese in both: `locale: LANG` would tag it English or Spanish, and a Chinese tag would set it by the Chinese rules (Kaiming punctuation, small kana free to start a line, 图 for 図, Chinese glyph forms in the PDF). From postext 1.30 the tag is also the language the text is shaped in (measured, painted and embedded), so any tag but 'ja' gives other glyph forms than the Japanese ones (the Chinese ones under a Chinese tag) and other line breaks. Write 'ja': it picks the Japan region (JLReq line breaking and punctuation, sesame emphasis marks, furigana spacing, 図 and 表 labels) and turns hyphenation off. The lint fails a text with kana under a zh or ko tag.

- A reading cannot stand over a blank yet: a ruby inside `[[…]]` is part of the hidden answer. The 漢字の書き取り exercise sets each reading on its own line and the box after it, three to a row in a `:::columns` group; on the vertical page the reading stands beside the box, as furigana do.
- Klee One ships 400 and 600 only: `boldFontWeight: 600` keeps every bold run in a cut that exists, the item numbers and the exercise numbers included.

## Credits

- Recipe: Ignacio Ferro ([@drnachio](https://github.com/drnachio))
- Images: A young tanuki in a yellow school hat holding a big pencil.: Generated With Diffusion Models, original
- Images: A fox cub in a red scarf reading a book.: Generated With Diffusion Models, original
- Type: Klee One (OFL-1.1), Zen Maru Gothic (OFL-1.1)
- Code: MIT · Sample content: CC-BY-4.0

## Related

- [Nº 174 · A puzzle page with the answers upside down](https://postext.dev/en/cookbook/puzzle-page-upside-down-answers.md): A children's magazine puzzle page: crossword, word search, riddle, story to order, matching and a mixed-up fact on cards, each with its answers upside down. · Level 2 (Intermediate) · Magazines & zines, Workbooks & exercises
- [Nº 124 · A school reader with furigana over every kanji](https://postext.dev/en/cookbook/jukugo-furigana-textbook.md): Niimi Nankichi’s “Gon the Fox” on a reader page: per-character, word and jukugo furigana, spaced 1:2:1 and running onto kana but never onto kanji. · Level 2 (Intermediate) · Textbooks
- [Nº 169 · One worksheet in ten school traditions](https://postext.dev/en/cookbook/school-traditions-worksheet.md): The same seven :::exercise fences in ten languages, each edition printed by an exercise style set the way that country's school books set exercises. · Level 2 (Intermediate) · Workbooks & exercises, Textbooks