# An illustrated timeline across a double page

> A spread page template lays a textbook timeline over two facing pages: a band runs across the spine, and two rows of cards trade width when one text runs long.

- HTML version: https://postext.dev/en/cookbook/illustrated-timeline-spread
- Recipe Nº 158 · Page & grid · Level 3 (Advanced) · Outputs: Canvas, PDF
- Genres: Textbooks
- Requires postext ≥ 1.38.0, postext-pdf ≥ 1.38.0 · tested with 1.38.0, postext-pdf 1.38.0 on 2026-10-17
- Pages: [48](https://postext.dev/cookbook/illustrated-timeline-spread/en/p01.webp?v=17fb78fe), [49](https://postext.dev/cookbook/illustrated-timeline-spread/en/p02.webp?v=17fb78fe)
- PDF: https://postext.dev/cookbook/illustrated-timeline-spread/en/illustrated-timeline-spread.pdf?v=17fb78fe
- Open in Sandbox: https://postext.dev/en/sandbox#recipe=illustrated-timeline-spread&lang=en (.postext: https://postext.dev/cookbook/illustrated-timeline-spread/en/illustrated-timeline-spread.postext)
- Last updated: 2026-10-17
- Other languages: [es](https://postext.dev/es/cookbook/illustrated-timeline-spread.md), [ca](https://postext.dev/ca/cookbook/illustrated-timeline-spread.md), [de](https://postext.dev/de/cookbook/illustrated-timeline-spread.md), [fr](https://postext.dev/fr/cookbook/illustrated-timeline-spread.md), [it](https://postext.dev/it/cookbook/illustrated-timeline-spread.md), [pt](https://postext.dev/pt/cookbook/illustrated-timeline-spread.md), [zh](https://postext.dev/zh/cookbook/illustrated-timeline-spread.md), [ja](https://postext.dev/ja/cookbook/illustrated-timeline-spread.md), [ar](https://postext.dev/ar/cookbook/illustrated-timeline-spread.md)

## In short

Two facing pages of a history textbook made as one: a coloured band crosses the middle of the book, and six picture cards under it share their width so the longest story gets the widest card.

## What you'll build

Pages 48 and 49 of a lower-secondary history book: *The paper road*, a thousand years of papermaking from Cai Lun's workshop to Keller's grindstone. The left page opens with the title and two paragraphs, the right page with a box on how a sheet was made by hand. Across the middle runs the timeline: an indigo band for Asia, a terracotta band for Europe that starts on the left page and crosses the spine. Under it, six cards with a picture each, hung from the band by a dot and a tick. The cards share their width: the 1844 card, with the longest story, takes width from its two neighbours (1 mm in Spanish, 7 mm in Japanese), and its dot moves with it. Every word is in the Markdown, in Spanish, English and Japanese.

**This recipe answers:**

- How do I lay out a timeline across a double page, with cards on both pages?
- How do I let a row of boxes share its width, so the one with the longest text gets wider?

## The short answer

One sheet for two pages, a band across the spine, two rows of cards.

```js
// script.js, lines 57–85
const pageTemplates = [{
  id: 'timeline',
  spread: true, // two facing pages laid as one sheet; it opens on a verso
  gutter: mm(10), // the band round the spine that frames keep off
  grid: { columns: 2, rows: ROWS, columnGap: mm(2 * PAGE.inner), rowGap: mm(ROW_GAP) },
  frames: [
    { name: 'title', takes: 'h1' },
    { name: 'lead', flow: true, fit: { minScale: 0.8 } },
    { name: 'box', style: 'box', grid: { col: 2, row: 1, rows: 4 }, height: 'fill',
      padding: { right: mm(66) }, fit: { minScale: 0.85 } },
    { name: 'box-picture', layer: 2, width: mm(56), placement: at('#box', 'top-right', -5, 10) },
    { name: 'band-1', style: 'band-asia', grid: { col: 1, row: 5 }, height: mm(BAND) },
    { name: 'band-2', style: 'band-europe', crossGutter: true, width: 'fill', height: mm(BAND),
      padding: { left: mm(2 * PAGE.inner + 4) }, // the colour crosses the fold, the words do not
      placement: at('#band-1', 'right-of') },
    ...cards.map(card),
    { name: 'colophon', style: 'colophon', optional: true, width: mm(170),
      placement: at('page', 'bottom-right', -PAGE.outer, -7) },
  ],
  groups: [
    { name: 'opening', kind: 'stack', grid: { col: 1, row: 1, rows: 4 }, gap: mm(4),
      frames: ['title', 'lead'] },
    // A card whose text runs past its drawn height takes width from its neighbours first;
    // only when they have none to give does the row grow taller.
    { name: 'asia', kind: 'row', gap: mm(5), frames: ['c1', 'c2', 'c3'] },
    { name: 'europe', kind: 'row', gap: mm(5), frames: ['c4', 'c5', 'c6'] },
  ],
  decoration: { elements: [ground(), ...cards.flatMap(marks)] },
}];
```

## Ingredients

**Teaches**

- [Spread templates](https://postext.dev/en/docs/composed-pages.md#spreads): A template with spread: true lays two facing pages as one sheet from a verso; a frame with crossGutter runs across the spine, and the others keep off the gutter band.
- [Frames that grow in a group](https://postext.dev/en/docs/composed-pages.md#when-the-text-grows): A stack or row of frames on a composed page: a frame as tall as its text, never below its minHeight, pushes the frames after it and what is anchored to them.
- [Decoration anchored to frames](https://postext.dev/en/docs/composed-pages.md#decoration-running-heads-and-layers): The rules, boxes, pictures and short texts of a template’s decoration are laid after its frames, so an element anchored to "#frame" follows that frame wherever its group moves or widens it.

**Also uses**

- [Composed pages](https://postext.dev/en/docs/composed-pages.md#composed-pages)
- [Numbered box tabs](https://postext.dev/en/docs/configuration-callouts.md#callout-styles)
- [Callout boxes](https://postext.dev/en/docs/configuration-callouts.md#callout-styles)
- [Anchoring design elements](https://postext.dev/en/docs/configuration-headers-footers.md#element-placement)
- [Running heads and folios](https://postext.dev/en/docs/configuration-headers-footers.md#headers--footers)
- [Mirrored margins](https://postext.dev/en/docs/configuration-page-layout.md#mirrored-margins)
- [Numbered lists](https://postext.dev/en/docs/configuration-lists-math.md#ordered-lists)
- [Chinese, Japanese and Korean fonts](https://postext.dev/en/docs/configuration-pdf-output.md#chinese-japanese-and-korean-fonts)
- [Semantic colour palette](https://postext.dev/en/docs/configuration-fonts-colors-viewers.md#color-palette)
- [Pages on a canvas](https://postext.dev/en/docs/configuration-programmatic-usage.md#rendering-a-page-to-a-bitmap)
- [PDF export](https://postext.dev/en/docs/configuration-pdf-output.md#generating-pdfs)
- [Figures exactly here](https://postext.dev/en/docs/document-format-resources.md#block-embed-optional-explicit-inline-placement)
- [Fonts embedded in the PDF](https://postext.dev/en/docs/configuration-pdf-output.md#why-a-font-provider)
- [Custom resource types](https://postext.dev/en/docs/configuration-resources.md#resource-types)
- [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), [`colorPalette`](https://postext.dev/en/docs/configuration-fonts-colors-viewers.md#color-palette), [`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), [`pageTemplates`](https://postext.dev/en/docs/configuration-composed-pages.md#page-templates), [`resourceTypes`](https://postext.dev/en/docs/configuration-resources.md#resource-types)

**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), [`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**

- Literata (OFL-1.1), Archivo (OFL-1.1), Noto Serif JP (OFL-1.1), Noto Sans JP (OFL-1.1)

## Method

### 1 · One sheet for two pages

```js
// script.js, lines 57–85
const pageTemplates = [{
  id: 'timeline',
  spread: true, // two facing pages laid as one sheet; it opens on a verso
  gutter: mm(10), // the band round the spine that frames keep off
  grid: { columns: 2, rows: ROWS, columnGap: mm(2 * PAGE.inner), rowGap: mm(ROW_GAP) },
  frames: [
    { name: 'title', takes: 'h1' },
    { name: 'lead', flow: true, fit: { minScale: 0.8 } },
    { name: 'box', style: 'box', grid: { col: 2, row: 1, rows: 4 }, height: 'fill',
      padding: { right: mm(66) }, fit: { minScale: 0.85 } },
    { name: 'box-picture', layer: 2, width: mm(56), placement: at('#box', 'top-right', -5, 10) },
    { name: 'band-1', style: 'band-asia', grid: { col: 1, row: 5 }, height: mm(BAND) },
    { name: 'band-2', style: 'band-europe', crossGutter: true, width: 'fill', height: mm(BAND),
      padding: { left: mm(2 * PAGE.inner + 4) }, // the colour crosses the fold, the words do not
      placement: at('#band-1', 'right-of') },
    ...cards.map(card),
    { name: 'colophon', style: 'colophon', optional: true, width: mm(170),
      placement: at('page', 'bottom-right', -PAGE.outer, -7) },
  ],
  groups: [
    { name: 'opening', kind: 'stack', grid: { col: 1, row: 1, rows: 4 }, gap: mm(4),
      frames: ['title', 'lead'] },
    // A card whose text runs past its drawn height takes width from its neighbours first;
    // only when they have none to give does the row grow taller.
    { name: 'asia', kind: 'row', gap: mm(5), frames: ['c1', 'c2', 'c3'] },
    { name: 'europe', kind: 'row', gap: mm(5), frames: ['c4', 'c5', 'c6'] },
  ],
  decoration: { elements: [ground(), ...cards.flatMap(marks)] },
}];
```

`spread: true` makes the template one sheet as wide as both pages, and the page fence says the same with `spread`. A spread opens on a verso, so the build passes `continuation: { pageIndexOffset: 1, pageNumbering: { startAt: 48 } }`: page 1 of this excerpt is the book's page 48, a left page, and no blank page comes first. The grid has one column per page, with a gap of twice the inner margin, so nothing but the band comes near the fold. The second band sets `crossGutter` and a left padding of 36 mm: its colour runs from the end of the first band across the spine, and its words start on the right page, where the layout reads them.

### 2 · Cards that trade width

```js
// script.js, lines 48–53
const cards = ['c1', 'c2', 'c3', 'c4', 'c5', 'c6'];
const card = (name, i) => ({ name, style: i < 3 ? 'card-asia' : 'card-europe',
  width: mm((HALF - 10) / 3), minWidth: mm(40), minHeight: mm(CARD),
  shrink: 1, // a card gives width to a neighbour whose text runs past the row
  ...(i % 3 === 0 && { placement: at('container', 'top-left', i ? HALF + 2 * PAGE.inner : 0,
    CARD_TOP) }) }); // where each row starts
```

Each row of three cards is a `row` group, and each card has a `minHeight`, the height it is drawn at, and an `auto` height above that. When a card's text runs past the row's height, it takes the fewest whole millimetres it needs from the neighbours with `shrink`, each of which keeps the width its own text still fits in. Only when they have nothing more to give does the row grow taller. In the Spanish edition the 1844 card takes 1 mm from 1282; in Japanese it takes 7 mm, 3 from 1150 and 4 from 1282; with every text 30 % longer, the bench test, the Spanish card takes 15 mm and the box and the lead set their text at 92.5 % and 85 %.

### 3 · Dots that follow the cards

```js
// script.js, lines 89–100
function marks(name, i) {
  const ink = col(i < 3 ? 'asia' : 'europe');
  return [
    { kind: 'rule', id: `${name}-tick`, direction: 'vertical', thickness: pt(1), color: ink,
      placement: { ...at(`#${name}`, 'top', 0, -DROP), size: { height: mm(DROP) } } },
    { kind: 'box', id: `${name}-dot`,
      placement: { ...at(`#${name}`, 'top', 0, -DROP + 0.6), size: { width: mm(4.4),
        height: mm(4.4) } },
      style: { backgroundColor: col('paper'), borderColor: ink, borderWidth: pt(1.6),
        borderRadius: mm(2.2) } },
  ];
}
```

The dots and ticks are the template's `decoration`, anchored to `#c1` … `#c6` at their `top` and raised by the distance to the band. Decoration is laid after the frames, so when a card moves or widens, its dot stays over its centre. The cream ground is decoration too, a box anchored to the bleed's foot whose height runs up to the foot of `#band-1` (`size: { height: { to: '#band-1', edge: 'bottom' } }`), so it follows the band.

### 4 · Pictures at the size they print

```js
// script.js, lines 261–303
const ART = {
  v105: t({ es: 'Un funcionario de la corte Han mira cómo un artesano saca de la tina un molde '
      + 'de bambú lleno de pasta, junto a corteza, trapos y redes viejas.',
    en: 'A Han court official watches a craftsman lift a bamboo mould full of pulp from a vat, '
      + 'beside bark, rags and old nets.',
    ja: '漢の役人が見守るなか、職人が竹のすき枠を漉き舟から引き上げる。そばに樹皮、ぼろ布、古い網。' }),
  v610: t({ es: 'Un monje enseña a dos cortesanos japoneses a sostener el molde sobre una tina, '
      + 'con ramas de kozo en una estera.',
    en: 'A monk shows two Japanese courtiers how to hold the mould over a tub, with kozo '
      + 'branches on a mat.',
    ja: '僧が二人の宮廷人に、桶の上ですき枠を持つ手つきを見せる。むしろの上に楮の枝。' }),
  v751: t({ es: 'Papeleros de Samarcanda junto a un canal; las hojas se secan al sol contra un '
      + 'muro de adobe.',
    en: 'Samarkand papermakers by a canal; the sheets dry in the sun against a mud-brick wall.',
    ja: '水路のそばで働くサマルカンドの紙すき職人。日干しれんがの壁に紙が張られて乾いている。' }),
  v1150: t({ es: 'Un taller de Xàtiva bajo el castillo: un operario golpea trapos en una pila '
      + 'de piedra y las hojas cuelgan de cuerdas.',
    en: 'A workshop in Xàtiva below the castle: a worker pounds rags in a stone trough and the '
      + 'sheets hang on ropes.',
    ja: '城の下のシャティバの工房。職人が石の槽でぼろ布をたたき、紙が綱につるされている。' }),
  v1282: t({ es: 'Un molino de Fabriano con su rueda hidráulica y sus mazos; un papelero mira '
      + 'una filigrana al trasluz.',
    en: 'A Fabriano mill with its water wheel and hammers; a papermaker holds a watermark up '
      + 'to the light.',
    ja: '水車と木づちのあるファブリアーノの製紙場。職人が紙を光にかざして透かしを見ている。' }),
  v1844: t({ es: 'Un artesano aprieta un tronco de abeto contra una muela que gira; debajo se '
      + 'amontonan las fibras.',
    en: 'A craftsman presses a spruce log against a turning grindstone; the fibres pile up '
      + 'below.',
    ja: '職人がトウヒの丸太を回る砥石に押し当て、その下に木の繊維が積もっていく。' }),
  forma: t({ es: 'Dos manos sacan de la tina el molde con una capa fina de fibras.',
    en: 'Two hands lift the mould from the vat with a thin layer of fibres on it.',
    ja: '両手ですき枠を引き上げる。網の上に繊維の薄い層ができている。' }),
};
const SIZE = { forma: [800, 800, 363] }; // pixels and ppi: 56 mm wide; the cards' are 46 mm
const resources = await Promise.all(Object.entries(ART).map(async ([id, altText]) => {
  const px = SIZE[id] ?? [1000, 667, 550];
  const fileId = `${id}-${px[0]}.jpg`;
  await loadImage(fileId, asset(fileId));
  return { id, typeId: 'picture', kind: 'bitmap', caption: '', altText, createdAt: 0,
    updatedAt: 0,
    bitmap: { fileId, format: 'jpeg', width: px[0], height: px[1], resolution: px[2] } };
}));
```

The vignettes are 1,000 px wide at 550 ppi, 46 mm on the page, and a picture is never enlarged: a card that widens keeps its picture and gives the room to its text. A card narrower than 53 mm (the picture plus 3.5 mm of padding on each side) sets its picture smaller, which the stress test shows in the Japanese edition: the 1150 and 1282 pictures at 85 %.

## 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/illustrated-timeline-spread

### script.js

```js
// ═══ Postext Cookbook · Nº 158 · An illustrated timeline across a double page ═══════
// https://postext.dev/en/cookbook/illustrated-timeline-spread
// Code: MIT · Text: original (CC BY 4.0) · Pictures: generated with diffusion models
// Fonts: Literata, Archivo, Noto Serif JP, Noto Sans JP (SIL OFL 1.1) · Needs postext ≥ 1.38.0
import {
  buildDocument, withLoadedFonts, renderPageToCanvas, registerResourceImage,
} from 'https://esm.sh/postext';
import { renderToPdf, decompressWoff2 } from 'https://esm.sh/postext-pdf';

const LANG = 'en'; // @lang: the language of the sample document ('es' | 'en' | 'ja')
const RECIPE = 'illustrated-timeline-spread';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// #region palette: one ink, an accent for each half of the timeline, a pale ground
const palette = {
  ink: '#22201d', // text
  asia: '#2f4f7a', // indigo: the Asian half of the timeline
  europe: '#a2412a', // terracotta: the European half
  ground: '#f1ebdf', // the cream under the cards
  rule: '#c9bfae', // hairlines and the card borders
  muted: '#6b6359', // running heads and the colophon
  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: 'europe (defaults)', value: { hex: palette.europe, model: 'hex' } },
];
// #endregion

const JA = LANG === 'ja';
const SERIF = JA ? 'Noto Serif JP' : 'Literata';
const SANS = JA ? 'Noto Sans JP' : 'Archivo';
// A Western textbook page is 210 × 280 mm; a Japanese one is AB判, 210 × 257 mm.
const PAGE = { w: 210, h: JA ? 257 : 280, top: 22, bottom: 20, inner: 16, outer: 15 };
const ROWS = 12;
const ROW_GAP = 3;
const ROW = (PAGE.h - PAGE.top - PAGE.bottom - (ROWS - 1) * ROW_GAP) / ROWS; // one grid row, mm
const HALF = PAGE.w - PAGE.inner - PAGE.outer; // the width of one page's half of the sheet
const BAND = 9; // the timeline band, in grid row 5
const DROP = ROW - BAND + ROW_GAP; // from the band's foot to the cards' heads
const CARD_TOP = 5 * (ROW + ROW_GAP); // grid row 6
// The drawn height of a card; 16 mm of the area stay free for a longer text.
const CARD = PAGE.h - PAGE.top - PAGE.bottom - CARD_TOP - 16;
const at = (to, edge, x = 0, y = 0) => ({ anchor: { to, edge }, offset: { x: mm(x), y: mm(y) } });

// #region cards: six cards at least one height tall that trade width with their neighbours
const cards = ['c1', 'c2', 'c3', 'c4', 'c5', 'c6'];
const card = (name, i) => ({ name, style: i < 3 ? 'card-asia' : 'card-europe',
  width: mm((HALF - 10) / 3), minWidth: mm(40), minHeight: mm(CARD),
  shrink: 1, // a card gives width to a neighbour whose text runs past the row
  ...(i % 3 === 0 && { placement: at('container', 'top-left', i ? HALF + 2 * PAGE.inner : 0,
    CARD_TOP) }) }); // where each row starts
// #endregion

// #region answer: one sheet for two pages, a band across the spine, two rows of cards
const pageTemplates = [{
  id: 'timeline',
  spread: true, // two facing pages laid as one sheet; it opens on a verso
  gutter: mm(10), // the band round the spine that frames keep off
  grid: { columns: 2, rows: ROWS, columnGap: mm(2 * PAGE.inner), rowGap: mm(ROW_GAP) },
  frames: [
    { name: 'title', takes: 'h1' },
    { name: 'lead', flow: true, fit: { minScale: 0.8 } },
    { name: 'box', style: 'box', grid: { col: 2, row: 1, rows: 4 }, height: 'fill',
      padding: { right: mm(66) }, fit: { minScale: 0.85 } },
    { name: 'box-picture', layer: 2, width: mm(56), placement: at('#box', 'top-right', -5, 10) },
    { name: 'band-1', style: 'band-asia', grid: { col: 1, row: 5 }, height: mm(BAND) },
    { name: 'band-2', style: 'band-europe', crossGutter: true, width: 'fill', height: mm(BAND),
      padding: { left: mm(2 * PAGE.inner + 4) }, // the colour crosses the fold, the words do not
      placement: at('#band-1', 'right-of') },
    ...cards.map(card),
    { name: 'colophon', style: 'colophon', optional: true, width: mm(170),
      placement: at('page', 'bottom-right', -PAGE.outer, -7) },
  ],
  groups: [
    { name: 'opening', kind: 'stack', grid: { col: 1, row: 1, rows: 4 }, gap: mm(4),
      frames: ['title', 'lead'] },
    // A card whose text runs past its drawn height takes width from its neighbours first;
    // only when they have none to give does the row grow taller.
    { name: 'asia', kind: 'row', gap: mm(5), frames: ['c1', 'c2', 'c3'] },
    { name: 'europe', kind: 'row', gap: mm(5), frames: ['c4', 'c5', 'c6'] },
  ],
  decoration: { elements: [ground(), ...cards.flatMap(marks)] },
}];
// #endregion

// #region marks: a dot under the band and a tick down to each card, anchored to the card
function marks(name, i) {
  const ink = col(i < 3 ? 'asia' : 'europe');
  return [
    { kind: 'rule', id: `${name}-tick`, direction: 'vertical', thickness: pt(1), color: ink,
      placement: { ...at(`#${name}`, 'top', 0, -DROP), size: { height: mm(DROP) } } },
    { kind: 'box', id: `${name}-dot`,
      placement: { ...at(`#${name}`, 'top', 0, -DROP + 0.6), size: { width: mm(4.4),
        height: mm(4.4) } },
      style: { backgroundColor: col('paper'), borderColor: ink, borderWidth: pt(1.6),
        borderRadius: mm(2.2) } },
  ];
}
// #endregion

// The cream ground under the cards: from the foot of the band down to the bleed.
function ground() {
  return { kind: 'box', id: 'ground', decorative: true,
    placement: { ...at('bleed', 'bottom-left'), size: { width: 'fill',
      height: { to: '#band-1', edge: 'bottom' } } },
    style: { backgroundColor: col('ground') } };
}

const tab = (ink) => ({ position: 'top-left', background: col(ink), color: col('paper'),
  fontFamily: SANS, fontSize: pt(10), fontWeight: 700, height: mm(6), paddingX: mm(2.6),
  offset: mm(3.5), inset: mm(0), rule: { enabled: false } });
const cardStyle = (id, ink) => ({ id, backgroundEnabled: true, background: col('paper'),
  border: { enabled: true, color: col('rule'), width: pt(0.5) }, borderRadius: mm(1.5),
  stripe: { enabled: true, side: 'top', width: pt(2.5), color: col(ink) },
  padding: { top: mm(8), right: mm(3.5), bottom: mm(3.5), left: mm(3.5) },
  label: tab(ink),
  body: { fontFamily: SERIF, fontSize: pt(JA ? 8.6 : 9.4), lineHeight: pt(JA ? 15 : 12.8),
    color: col('ink'), boldColor: col(ink), italicColor: col('ink'),
    textAlign: JA ? 'justify' : 'left', hyphenation: !JA, firstLineIndent: pt(0),
    boldFontWeight: 700 } });
const bandStyle = (id, ink) => ({ id, backgroundEnabled: true, background: col(ink),
  border: { enabled: false }, padding: { top: mm(1.6), right: mm(4), bottom: mm(1), left: mm(4) },
  body: { fontFamily: SANS, fontSize: pt(9.5), lineHeight: pt(12), fontWeight: 700,
    color: col('paper'), firstLineIndent: pt(0) } });

const head = (id, content, parity, edge, x) => ({ kind: 'text', id, content, parity,
  fontFamily: SANS, fontSize: pt(8), fontWeight: 600, letterSpacing: pt(JA ? 0 : 0.8),
  color: col('muted'), placement: at('page', edge, x, 11) });
const folio = (id, parity, edge, x) => ({ kind: 'text', id, content: '{pageNumber}', parity,
  fontFamily: SANS, fontSize: pt(9), fontWeight: 700, color: col('ink'),
  placement: at('page', edge, x, -10) });

const config = {
  locale: t({ es: 'es', en: 'en-gb', ja: 'ja' }),
  resourceTypes: [{ id: 'picture', name: t({ es: 'Ilustración', en: 'Illustration',
    ja: 'イラスト' }), shortLabel: '', numberingTemplate: '', resetOn: 'never',
  counterFormat: 'decimal', captionPrefix: '', defaultPlacement: { position: 'here' } }],
  colorPalette,
  page: {
    sizePreset: 'custom', width: mm(PAGE.w), height: mm(PAGE.h), dpi: 150,
    margins: { top: mm(PAGE.top), bottom: mm(PAGE.bottom), left: mm(PAGE.inner),
      right: mm(PAGE.outer), mirror: true },
  },
  layout: { layoutType: 'single' },
  bodyText: {
    fontFamily: SERIF, fontSize: pt(JA ? 10.5 : 12.4), lineHeight: pt(JA ? 18.5 : 17),
    paragraphSpacing: !JA,
    color: col('ink'), boldColor: col('ink'), italicColor: col('ink'),
    referenceColor: col('ink'), textAlign: JA ? 'justify' : 'left',
    firstLineIndent: JA ? em(1) : pt(0), // Japanese paragraphs open with a one-character indent
    hyphenation: { enabled: !JA },
  },
  headings: {
    fontFamily: SANS, color: col('ink'), fontWeight: 800,
    levels: [{ level: 1, fontSize: pt(JA ? 44 : 58), lineHeight: pt(JA ? 54 : 60),
      color: col('asia'), marginTop: pt(0), marginBottom: pt(0),
      breakBefore: { enabled: false } }],
  },
  orderedLists: { numberFormat: 'arabic', color: col('europe'), fontWeight: 700 },
  calloutStyles: [
    { id: 'box', backgroundEnabled: true, background: col('paper'),
      border: { enabled: true, color: col('rule'), width: pt(0.5) },
      borderRadius: mm(1.5), padding: { top: mm(9), right: mm(5), bottom: mm(4), left: mm(5) },
      label: tab('europe'),
      body: { fontFamily: SERIF, fontSize: pt(JA ? 9.5 : 10.4), lineHeight: pt(JA ? 16.5 : 14.2),
        color: col('ink'), boldColor: col('ink'), italicColor: col('ink'), textAlign: 'left',
        firstLineIndent: pt(0), paragraphSpacing: true },
      lists: { color: col('europe'), gap: mm(1.5), itemSpacing: mm(1.2) } },
    cardStyle('card-asia', 'asia'), cardStyle('card-europe', 'europe'),
    bandStyle('band-asia', 'asia'), bandStyle('band-europe', 'europe'),
    { id: 'colophon', backgroundEnabled: false, border: { enabled: false },
      padding: { top: mm(0), right: mm(0), bottom: mm(0), left: mm(0) },
      body: { fontFamily: SANS, fontSize: pt(6.5), lineHeight: pt(8), color: col('muted'),
        firstLineIndent: pt(0) } },
  ],
  header: { elements: [
    head('subject', '{attr.subject}', 'even', 'top-left', PAGE.outer),
    head('unit', '{attr.unit}', 'odd', 'top-right', -PAGE.outer),
  ] },
  footer: { elements: [
    folio('verso-folio', 'even', 'bottom-left', PAGE.outer),
    folio('recto-folio', 'odd', 'bottom-right', -PAGE.outer),
  ] },
  pageTemplates,
};
// The spread opens on a verso: page 1 of this excerpt is book page 48.
const continuation = { pageIndexOffset: 1, pageNumbering: { startAt: 48 } };

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`::::page{template="timeline" spread subject="History · Year 8" unit="Unit 5 · Trade routes"}
# The paper road

For centuries, making paper was a craft kept in Chinese workshops. It took more than a thousand years to travel from there to the mills of Europe.

Every people who learnt it changed the recipe to suit what they had to hand: mulberry bark in China, kozo in Japan, flax and rags in Samarkand and al-Andalus, and wood in the nineteenth century.

:::frame{slot="box" label="How a sheet was made"}
1. The fibres are chopped and left to soak until they break down into a pulp.
2. The mould, a fine screen on a wooden frame, is dipped into the vat and lifted out full of pulp.
3. The mould is shaken: the water drains away and the fibres lock together in an even layer.
4. The sheet is pressed between felts and hung up to dry.

The wires of the mould leave their print in the sheet: they are the fine lines you see when you hold paper up to the light.
:::

::resource{id="forma" slot="box-picture"}

:::frame{slot="band-1"}
In Asia, from the 2nd to the 8th century
:::

:::frame{slot="band-2"}
Around the Mediterranean and in Europe, from the 12th to the 19th century
:::

:::frame{slot="c1" label="105"}
::resource{id="v105"}

**China.** Cai Lun, an official at the Han court, presents the emperor with paper made from mulberry bark, scraps of hemp, rags and old fishing nets. It costs less than silk and weighs far less than strips of bamboo. Archaeologists have found Chinese paper two centuries older, but Cai Lun's is the one copied across the empire.
:::

:::frame{slot="c2" label="610"}
::resource{id="v610"}

**Japan.** According to the chronicle *Nihon shoki*, the monk Damjing, from the Korean kingdom of Goguryeo, teaches the court how to make paper and ink. Japanese papermakers turn the bark of the kozo shrub into *washi*, thin and very strong. The Shōsōin in Nara still keeps household registers written on paper in 702.
:::

:::frame{slot="c3" label="751"}
::resource{id="v751"}

**Samarkand.** A tradition says that after the Battle of Talas, Chinese prisoners taught the craft in this Silk Road city. Samarkand's papermakers use flax and cotton rags. By about 800, Baghdad has workshops of its own, and paper replaces parchment in the caliph's archives.
:::

:::frame{slot="c4" label="1150"}
::resource{id="v1150"}

**Xàtiva.** The geographer al-Idrisi writes that this town of al-Andalus makes a paper with no equal anywhere in the world, sold to East and West. When James I takes the town in 1244, the workshops carry on.
:::

:::frame{slot="c5" label="1282"}
::resource{id="v1282"}

**Fabriano.** The mills of this Italian town use the river to drive hammers that beat rags to pulp. They size their sheets with gelatine, which stops the ink from spreading, and mark them with a watermark, a design that only shows against the light. By the 14th century, Italian paper is sold across half of Europe.
:::

:::frame{slot="c6" label="1844"}
::resource{id="v1844"}

**Saxony.** After printing come the newspapers, and there are no longer rags enough for so much paper. In 1798, Louis-Nicolas Robert had built a machine in France that made one continuous sheet, with no mould. In 1844 the weaver Friedrich Gottlob Keller presses spruce logs against a grindstone and gets wood pulp. From then on paper is cheap and plentiful, and a daily paper costs no more than a loaf of bread.
:::

:::frame{slot="colophon"}
Set in Literata and Archivo (SIL OFL) · Original text (CC BY 4.0) · Illustrations generated with diffusion models
:::
::::
`; // content.<lang>.md, inlined by the Cookbook

// #region art: seven pictures at the size they print, with what each shows
const ART = {
  v105: t({ es: 'Un funcionario de la corte Han mira cómo un artesano saca de la tina un molde '
      + 'de bambú lleno de pasta, junto a corteza, trapos y redes viejas.',
    en: 'A Han court official watches a craftsman lift a bamboo mould full of pulp from a vat, '
      + 'beside bark, rags and old nets.',
    ja: '漢の役人が見守るなか、職人が竹のすき枠を漉き舟から引き上げる。そばに樹皮、ぼろ布、古い網。' }),
  v610: t({ es: 'Un monje enseña a dos cortesanos japoneses a sostener el molde sobre una tina, '
      + 'con ramas de kozo en una estera.',
    en: 'A monk shows two Japanese courtiers how to hold the mould over a tub, with kozo '
      + 'branches on a mat.',
    ja: '僧が二人の宮廷人に、桶の上ですき枠を持つ手つきを見せる。むしろの上に楮の枝。' }),
  v751: t({ es: 'Papeleros de Samarcanda junto a un canal; las hojas se secan al sol contra un '
      + 'muro de adobe.',
    en: 'Samarkand papermakers by a canal; the sheets dry in the sun against a mud-brick wall.',
    ja: '水路のそばで働くサマルカンドの紙すき職人。日干しれんがの壁に紙が張られて乾いている。' }),
  v1150: t({ es: 'Un taller de Xàtiva bajo el castillo: un operario golpea trapos en una pila '
      + 'de piedra y las hojas cuelgan de cuerdas.',
    en: 'A workshop in Xàtiva below the castle: a worker pounds rags in a stone trough and the '
      + 'sheets hang on ropes.',
    ja: '城の下のシャティバの工房。職人が石の槽でぼろ布をたたき、紙が綱につるされている。' }),
  v1282: t({ es: 'Un molino de Fabriano con su rueda hidráulica y sus mazos; un papelero mira '
      + 'una filigrana al trasluz.',
    en: 'A Fabriano mill with its water wheel and hammers; a papermaker holds a watermark up '
      + 'to the light.',
    ja: '水車と木づちのあるファブリアーノの製紙場。職人が紙を光にかざして透かしを見ている。' }),
  v1844: t({ es: 'Un artesano aprieta un tronco de abeto contra una muela que gira; debajo se '
      + 'amontonan las fibras.',
    en: 'A craftsman presses a spruce log against a turning grindstone; the fibres pile up '
      + 'below.',
    ja: '職人がトウヒの丸太を回る砥石に押し当て、その下に木の繊維が積もっていく。' }),
  forma: t({ es: 'Dos manos sacan de la tina el molde con una capa fina de fibras.',
    en: 'Two hands lift the mould from the vat with a thin layer of fibres on it.',
    ja: '両手ですき枠を引き上げる。網の上に繊維の薄い層ができている。' }),
};
const SIZE = { forma: [800, 800, 363] }; // pixels and ppi: 56 mm wide; the cards' are 46 mm
const resources = await Promise.all(Object.entries(ART).map(async ([id, altText]) => {
  const px = SIZE[id] ?? [1000, 667, 550];
  const fileId = `${id}-${px[0]}.jpg`;
  await loadImage(fileId, asset(fileId));
  return { id, typeId: 'picture', kind: 'bitmap', caption: '', altText, createdAt: 0,
    updatedAt: 0,
    bitmap: { fileId, format: 'jpeg', width: px[0], height: px[1], resolution: px[2] } };
}));
// #endregion

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
const FONTS = {
  Literata: ['400', '400i', '700'], Archivo: ['400', '600', '700', '800'], // es, en
  'Noto Serif JP': ['400', '700'], 'Noto Sans JP': ['400', '600', '700', '800'], // ja
};

// ─── 4 · Build & show ───────────────────────────────────────────────────────
await loadFonts(FONTS, markdown); // the latin files of every face
await loadCjkFonts({ [SERIF]: FONTS[SERIF], [SANS]: FONTS[SANS] }, markdown); // ja only
const doc = await withLoadedFonts(
  () => buildDocument({ markdown, resources, continuation }, config),
  { ...kitFonts(FONTS), text: markdown });
showPages(doc, { title: t({ es: 'Una cronología ilustrada a doble página',
  en: 'An illustrated timeline across a double page', ja: '見開きの絵入り年表' }) });
offerPdf(() => renderToPdf(doc, { 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 (prepareFonts,
// buildDocumentWithFonts) and asks the kit for the files: Fontsource's, the
// files the PDF embeds too.

/** The options of buildDocumentWithFonts / prepareFonts / withLoadedFonts:
 *  the Fontsource resolver, and the faces of FONTS loaded with the ones the
 *  config names. 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 Fontsource files, in a fixed order: latin, then latin-ext and greek
 *  when `text` needs them and the family ships them (kitSubsetsFor), each with
 *  its unicode-range. Null for a weight or slant Fontsource does not ship. */
async function fontsourceResolver(family, weight, style, { text = '' } = {}) {
  const id = fontsourceId(family);
  const meta = await fontsourceMeta(family);
  if (meta && !(meta.weights.includes(weight) && meta.styles.includes(style))) 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],
  }));
}

/** The unicode-range of each Fontsource file the kit loads (a function: the
 *  kit is inlined after the pen's code, which runs before a const would be set). */
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, which add their own files: the
 *  faces of `faces` = { 'Family Name': ['400', '400i', '700'] }. `text` is the sample:
 *  č ł † α χ also load latin-ext and greek files (kitSubsetsFor). With
 *  `optional`, a face Fontsource does not ship is skipped instead of failing.
 *  The files are added once all have loaded, in the order asked (latin, then
 *  latin-ext, then greek), whatever order they arrive in: the last one added
 *  wins a character two files hold. Resolves to the number of faces added. */
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?.weights.includes(weight) && meta.styles.includes(style))) 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 family, weight and style (fonts.check() would
 *  also say yes for families nobody declared). */
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) {
  fontsourceMeta.cache ??= new Map();
  const id = fontsourceId(family);
  if (!fontsourceMeta.cache.has(id)) {
    fontsourceMeta.cache.set(id, fetch(`https://api.fontsource.org/v1/fonts/${id}`)
      .then((res) => (res.ok ? res.json() : null), () => null));
  }
  return fontsourceMeta.cache.get(id);
}

// ─── 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, 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 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 && !meta.styles.includes('italic') ? 'normal' : style;
  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

### Keep the cards the same width

With `shrink: 0` no card gives width: the row grows taller instead, all three cards together, and its foot moves down the page.

```diff
-  shrink: 1, // a card gives width to a neighbour whose text runs past the row
+  shrink: 0,
```

## Pitfalls

- A card with a fixed `height` takes no part in the width trade, since it never runs past the row: give the cards a `minHeight`, as here, and leave the height `auto`.
- A size that runs to an edge of another box counts from the element's own anchor point: the ground is anchored to the bleed's foot and grows up to `#band-1`. An edge behind the anchor gives a height of 0.

## Credits

- Recipe: Ignacio Ferro ([@drnachio](https://github.com/drnachio))
- Text: The paper road, a double-page timeline written for this recipe in Spanish, English and Japanese: Postext Cookbook, CC-BY-4.0
- Images: A Han court official watches a craftsman lift a bamboo mould from a vat.: Generated With Diffusion Models, original
- Images: A monk shows two Japanese courtiers how to hold a papermaking mould.: Generated With Diffusion Models, original
- Images: Papermakers by a canal in Samarkand, sheets drying on a wall.: Generated With Diffusion Models, original
- Images: A paper workshop below the castle of Xàtiva.: Generated With Diffusion Models, original
- Images: A Fabriano mill with its water wheel; a sheet held up to the light.: Generated With Diffusion Models, original
- Images: A craftsman grinds a spruce log against a stone into wood pulp.: Generated With Diffusion Models, original
- Images: Two hands lift a papermaker's mould from a vat of pulp.: Generated With Diffusion Models, original
- Type: Literata (OFL-1.1), Archivo (OFL-1.1), Noto Serif JP (OFL-1.1), Noto Sans JP (OFL-1.1)
- Code: MIT · Sample content: CC-BY-4.0

## Related

- [Nº 154 · One comic page across a double spread](https://postext.dev/en/cookbook/comic-double-spread.md): A :::page with the spread flag lays one split tree over two facing pages: a panorama crosses the spine, and the tier below splits on the fold. · Level 2 (Intermediate) · Comics
- [Nº 159 · Activity book with boxes that grow](https://postext.dev/en/cookbook/activity-book-growing-boxes.md): A science activity book on page templates: boxes in a stack grow with their text, answer lines sit on empty frames, a project goes on overleaf. · Level 3 (Advanced) · Workbooks & exercises, Textbooks
- [Nº 085 · A woodblock leaf: double frame, rules and centre strip](https://postext.dev/en/cookbook/woodblock-leaf.md): Zhu Xi's commentary on the Analects set as a woodblock printed it: a leaf to a spread, a double frame, a rule between columns and the centre strip on the fold. · Level 2 (Intermediate) · Textbooks