简单来说

把历史课本里相对的两页当作一页来排：一条彩色的带子横过书的中间，下面六张带插图的卡片分配宽度，故事最长的那张卡片最宽。

成品一览

初中历史课本的第48、49页：《纸的旅程》，从蔡伦的作坊到凯勒的磨石，造纸术走过的一千年。左页是标题和两段导语，右页是一个方框，讲手工抄一张纸的步骤。年表从两页中间横穿而过：亚洲一段用靛蓝色带，欧洲一段用赭红色带，后者从左页开始，跨过书脊。色带下面挂着六张卡片，每张有一幅插图，用一个圆点和一条短线连到色带上。这些卡片互相分配宽度：1844年那张故事最长，从两边的卡片借来宽度（西班牙语版1毫米，日语版7毫米），它的圆点也跟着移动。所有文字都写在Markdown里，有西班牙语、英语和日语三个版本；本页显示西班牙语版。

这道食谱解答

怎样把年表排成跨页，让一条色带跨过书脊，卡片分布在两页上？
怎样让一行方框分配宽度，文字最长的那个变宽？

简短回答

script.js · 第57–85行在完整代码中

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)] },
}];

用料

功能: 跨页模板组内随文字变高的框锚定在框上的装饰模板页带编号的框标签标注框锚定设计元素书眉与页码对称页边距编号列表中日韩字体语义调色板在Canvas上绘制页面导出PDF
还用到: 图就放在这里嵌入PDF的字体自定义资源类型作为资源的图和表
类型: Literata, Archivo, Noto Serif JP, Noto Sans JP（SIL OFL 1.1）
素材: forma-800.jpg
v105-1000.jpg
v1150-1000.jpg
v1282-1000.jpg
v1844-1000.jpg
v610-1000.jpg
v751-1000.jpg
A Han court official watches a craftsman lift a bamboo mould from a vat. (Generated With Diffusion Models, 原创)
A monk shows two Japanese courtiers how to hold a papermaking mould. (Generated With Diffusion Models, 原创)
Papermakers by a canal in Samarkand, sheets drying on a wall. (Generated With Diffusion Models, 原创)
A paper workshop below the castle of Xàtiva. (Generated With Diffusion Models, 原创)
A Fabriano mill with its water wheel; a sheet held up to the light. (Generated With Diffusion Models, 原创)
A craftsman grinds a spruce log against a stone into wood pulp. (Generated With Diffusion Models, 原创)
Two hands lift a papermaker's mould from a vat of pulp. (Generated With Diffusion Models, 原创)
API: buildDocumentdecompressWoff2registerResourceImagerenderPageToCanvasrenderToPdfwithLoadedFonts

做法

#1 · 两页共用一张纸

script.js · 第57–85行在完整代码中

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把模板变成一张和两页一样宽的纸，页面块也用spread标明这一点。跨页从左页开始，所以排版时传入continuation: { pageIndexOffset: 1, pageNumbering: { startAt: 48 } }：这段节选的第1页就是书的第48页，是左页，前面不需要空白页。网格每页一栏，两栏之间的间距是内侧页边距的两倍，所以只有色带靠近书脊。第二条色带设了crossGutter和36毫米的左内边距：颜色接着第一条色带跨过书脊，文字从右页开始，排版也在右页读取这些文字。

#2 · 互相分配宽度的卡片

script.js · 第48–53行在完整代码中

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

每行三张卡片是一个row组，每张卡片有minHeight，也就是它画出来的高度，超过这个高度就是auto。某张卡片的文字超出这一行的高度时，它向带shrink的相邻卡片借来所需的最少整毫米数，每张相邻卡片都保留足够放下自己文字的宽度。只有借不到时，这一行才往下长。西班牙语版里，1844年的卡片从1282年那张借1毫米；日语版里借7毫米，从1150年那张借3毫米，从1282年那张借4毫米。把所有文字加长30%（测试台的压力测试）时，西班牙语版借到15毫米，方框和导语的文字分别缩到92.5%和85%。

#3 · 跟着卡片走的圆点

script.js · 第89–100行在完整代码中

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) } },
  ];
}

圆点和短线是模板的装饰（decoration），以上边（top）锚定在#c1 … #c6上，再往上提到色带的位置。装饰在框排好之后才放，所以卡片移动或变宽时，圆点始终在它的正中上方。米色的底也是装饰：一个锚定在出血底边的方块，高度向上到#band-1的底边为止（size: { height: { to: '#band-1', edge: 'bottom' } }），所以它跟着色带走。

#4 · 按印刷尺寸放的插图

script.js · 第261–303行在完整代码中

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] } };
}));

插图宽1000像素，分辨率550 ppi，在页面上宽46毫米，而图片从不放大：变宽的卡片保持插图大小，把多出来的地方留给文字。比53毫米（插图加两侧各3.5毫米的内边距）窄的卡片会把插图缩小，测试台的压力测试在日语版里就看到了：1150年和1282年两张的插图缩到85%。

完整食谱

沙盒

// ═══ 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 = 'es'; // @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="Geografía e Historia · 2.º ESO" unit="Unidad 5 · Los caminos del comercio"}
Markdown样例 · 65行 · content.es.md
# La ruta del papel

Hacer papel fue durante siglos un secreto de los talleres chinos. Desde allí, el oficio tardó más de mil años en llegar a los molinos de Europa.

Cada pueblo que lo aprendió cambió la receta según lo que tenía a mano: corteza de morera en China, kozo en Japón, lino y trapos en Samarcanda y en al-Ándalus y, en el siglo XIX, madera.

:::frame{slot="box" label="Así se hacía una hoja"}
1. Se trituran las fibras y se dejan en remojo hasta que forman una pasta.
2. Se mete en la tina el molde, una rejilla fina en un marco de madera, y se saca cargado de pasta.
3. Se sacude el molde: el agua escurre y las fibras se traban en una capa uniforme.
4. La hoja se prensa entre fieltros y se cuelga para que se seque.

Los hilos del molde dejan su huella en la hoja: son las líneas finas que se ven al mirar el papel a contraluz.
:::

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

:::frame{slot="band-1"}
En Asia, del siglo II al VIII
:::

:::frame{slot="band-2"}
En el Mediterráneo y en Europa, del siglo XII al XIX
:::

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

**China.** Cai Lun, funcionario de la corte de los Han, presenta al emperador un papel hecho con corteza de morera, restos de cáñamo, trapos y redes de pesca viejas. Cuesta menos que la seda y pesa mucho menos que las tablillas de bambú. Los arqueólogos han encontrado papeles chinos dos siglos más antiguos, pero el de Cai Lun es el que se copia en todo el imperio.
:::

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

**Japón.** Según la crónica *Nihon shoki*, el monje Damjing, llegado del reino coreano de Goguryeo, enseña en la corte a fabricar papel y tinta. Con la corteza del kozo, los japoneses consiguen el *washi*, fino y muy resistente. En el Shōsōin de Nara se guardan todavía padrones de familias escritos en papel del año 702.
:::

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

**Samarcanda.** Una tradición cuenta que, tras la batalla de Talas, unos prisioneros chinos enseñaron el oficio en esta ciudad de la Ruta de la Seda. Los papeleros de Samarcanda usan lino y trapos de algodón. Hacia el año 800, Bagdad ya tiene talleres, y el papel sustituye al pergamino en los archivos del califa.
:::

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

**Xàtiva.** El geógrafo al-Idrisi escribe que en esta ciudad de al-Ándalus se hace un papel que no tiene igual en todo el mundo y que se vende a Oriente y a Occidente. Cuando Jaime I conquista la ciudad en 1244, los talleres siguen trabajando.
:::

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

**Fabriano.** Los molinos de esta ciudad italiana usan la fuerza del río para mover mazos que deshacen los trapos. Encolan las hojas con gelatina, que impide que la tinta se corra, y marcan los pliegos con una filigrana, un dibujo que solo se ve al trasluz. En el siglo XIV, el papel italiano se vende en media Europa.
:::

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

**Sajonia.** Después de la imprenta llegan los periódicos, y los trapos ya no bastan para tanto papel. En 1798, Louis-Nicolas Robert había construido en Francia una máquina que fabricaba una hoja continua, sin molde. En 1844, el tejedor Friedrich Gottlob Keller aprieta troncos de abeto contra una muela de piedra y obtiene pasta de madera. A partir de entonces el papel se vuelve barato y abundante, y un diario cuesta lo que una barra de pan.
:::

:::frame{slot="colophon"}
Compuesto en Literata y Archivo (SIL OFL) · Texto original (CC BY 4.0) · Ilustraciones generadas con modelos de difusión
:::
::::
`; // 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`);

工具包 · core, fonts, viewer, pdf, images, cjk：每道食谱都相同 · 504行
// ─── 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 ───────────────────────────────────────────────────────────────────────

组合好的script.js可以直接运行：把它粘贴到任何页面的模块脚本中，或在CodePen上打开这道食谱。 GitHub上的食谱文件夹 ↗ (在新标签页中打开)

变化

#让卡片保持同样宽度

设成shrink: 0后，没有卡片让出宽度：这一行改为往下长，三张卡片一起，行的下沿随之下移。

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

常见问题

固定height的卡片不参与宽度的分配，因为它从不超出这一行：请像这里一样给卡片设minHeight，高度留作auto。
延伸到另一个方框边缘的尺寸，从元素自己的锚点算起：米色的底锚定在出血底边，向上长到#band-1。位于锚点后方的边，得到的高度是0。

致谢

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

编辑这篇说明 ↗ (在新标签页中打开)GitHub上的食谱文件夹 ↗ (在新标签页中打开)

简单来说

#成品一览

#简短回答

#用料

#做法

#1 · 两页共用一张纸

#2 · 互相分配宽度的卡片

#3 · 跟着卡片走的圆点

#4 · 按印刷尺寸放的插图

#完整食谱

#变化

#让卡片保持同样宽度

#常见问题

#致谢

排版食谱中的更多内容

横跨两页的一页漫画

活动框随文字变高的练习册

刻本书叶：四周双边、界行与版心

成品一览

简短回答

用料

做法

完整食谱

变化

常见问题

致谢