مستند رسمي صيني وفق GB/T 9704

// ═══ Postext Cookbook · Nº 082 · A Chinese official document to GB/T 9704 ═════════
// https://postext.dev/en/cookbook/chinese-official-document
// Code: MIT · Text: a fictitious notice written for the recipe (CC BY 4.0) · Pictures: none
// Fonts: Noto Serif SC, Noto Sans SC, LXGW WenKai TC (SIL OFL 1.1) · Needs postext ≥ 1.9.0
import {
  buildDocument, renderPageToCanvas, clearMeasurementCache, parseTSV, mergeCells,
} from 'https://esm.sh/postext';
import { renderToPdf, decompressWoff2 } from 'https://esm.sh/postext-pdf';

const LANG = 'en'; // @lang: the language of the sample document ('en' | 'es')
const RECIPE = 'chinese-official-document';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// GB/T 9704 prints everything black but the letterhead: the issuer's name and a rule in red.
const palette = { ink: '#161616', red: '#d2161e', muted: '#8a8580', paper: '#ffffff' };
const col = (id) => ({ hex: palette[id], model: 'hex', paletteId: id });
const colorPalette = Object.entries({ ...palette, 'main-color': palette.red })
  .map(([id, hex]) => ({ id, name: id, value: { hex, model: 'hex' } }));
const SONG = 'Noto Serif SC'; // 宋: the text (in place of 仿宋, see the write-up) and 小标宋
const HEI = 'Noto Sans SC'; // 黑: the 一、 heads, the annex label, the specimen stamp
const KAI = 'LXGW WenKai TC'; // 楷: the （一） heads
const MM = 25.4 / 72; // mm per pt
const [BODY, LEAD, CHARS, LINES] = [15.75, 29, 28, 22]; // 三号 on 29 pt lines, 28 × 22 of them
const AREA = { w: CHARS * BODY * MM, h: LINES * LEAD * MM }; // 155.6 × 225.1 mm: the 版心
const [TOP, INNER] = [37, 28]; // mm: 天头 and 订口, the head and binding margins

// #region answer: A4, 28 characters × 22 lines of 三号, full-width marks on the grid
const cjk = {
  grid: { enabled: true, charsPerLine: CHARS, linesPerPage: LINES }, // 28 ems × 22 lines
  // Every mark takes a whole cell, as on the standard's grid, and never gives any of it up.
  punctuationWidth: 'fullwidth', compressAdjacent: false, trimLineStart: false,
  hangingPunctuation: 'allow', // a ， that may not open a line hangs past the 28th cell
  latinSpacing: em(0), // 〔2026〕7号 and 2026年9月28日 set solid, as the standard prints them
};
const page = {
  // 144 dpi is 2 px to the point: the 29 pt lines add up with no rounding (see Pitfalls).
  width: mm(210), height: mm(297), dpi: 144, backgroundColor: col('paper'),
  // With the grid on, margins are minimums. These leave 28 × 22 cells and 0.02 mm to share,
  // so the type area sits 37 mm under the head and 28 mm from the binding edge.
  margins: { top: mm(TOP), bottom: mm(297 - TOP - AREA.h - 0.02), left: mm(INNER),
    right: mm(210 - INNER - AREA.w - 0.02), mirror: true },
};
const bodyText = {
  fontFamily: SONG, fontSize: pt(BODY), lineHeight: pt(LEAD), color: col('ink'),
  boldColor: col('ink'), italicColor: col('ink'), referenceColor: col('ink'),
  textAlign: 'justify', // a short line spreads between its characters, never between words
  firstLineIndent: em(2), indentAfterHeading: true, // 左空二字，回行顶格
};
// #endregion

// #region levels: 一、 in Hei, （一） in Kai, 1. and （1） in the text face, all 三号 on the grid
// One line each at the body size, nothing above or below: every head stays on the grid.
// Headings have no indent of their own, so two ideographic spaces open each template.
const level = (n, fontFamily, fontWeight, numberingTemplate) => ({ level: n, fontFamily,
  fontWeight, numberingTemplate, numberSeparator: '', fontSize: pt(BODY), lineHeight: pt(LEAD),
  marginTop: pt(0), marginBottom: pt(0) });
const levels = [
  level(2, HEI, 500, '　　{2:一}、'), // 一 is the informal numeral in the document's script
  level(3, KAI, 400, '　　（{3:一}）'),
  level(4, SONG, 400, '　　{4}.'),
  level(5, SONG, 400, '　　（{5}）'),
];
// #endregion

// #region letterhead: the 版头 of page 1, placed line by line on the grid
const LINE = LEAD * MM; // 10.23 mm
const lineTop = (n) => (n - 1) * LINE; // mm from the top of the type area to grid line n
const face = (fontFamily, size, fontWeight, colour, lineHeight = LEAD / size) => ({
  fontFamily, fontSize: pt(size), fontWeight, color: col(colour), lineHeight });
// A text y mm down the type area, x mm in from its edge, as wide as the type area.
const text = (id, content, look, y, { edge = 'top-left', x = 0, width = AREA.w, ...more } = {},
) => ({ kind: 'text', id, content, ...look, align: 'center', overflow: 'wrap', ...more,
  placement: { anchor: { to: 'container', edge }, offset: { x: mm(x), y: mm(y) },
    size: { width: width === 'auto' ? 'auto' : mm(width) } } }); // wrap, not '…'
const rule = (id, y, thickness, colour = 'ink', reserve = false) => ({ kind: 'rule', id, reserve,
  direction: 'horizontal', thickness, color: col(colour), placement: { anchor: { to: 'container',
    edge: 'top-left' }, offset: { y: mm(y) }, size: { width: mm(AREA.w) } } });
const PAD = { left: pt(5), right: pt(5) }; // the specimen stamp's: not a GB/T 9704 element
const letterhead = { enabled: true, minHeight: pt(13 * LEAD), slot: { elements: [
  text('copy', '{attr.copy}', face(SONG, BODY, 400, 'ink'), lineTop(1), { align: 'left' }),
  text('stamp', '样　张', face(HEI, BODY, 500, 'red', 1.3), lineTop(1) + 1.5, { edge: 'top-right',
    width: 'auto', box: { borderColor: col('red'), borderWidth: pt(1), padding: PAD } }),
  // The name's ink starts 35 mm down, 0.07 em over its box; at 46 pt it ends in line 5.
  text('issuer', '{attr.issuer}文件', face(SONG, 46, 900, 'red', 1), 35 + 0.07 * 46 * MM),
  // The number two blank lines under the name; the red rule 4 mm under its characters.
  text('number', '{attr.number}', face(SONG, BODY, 400, 'ink'), lineTop(8)),
  rule('red-rule', lineTop(8) + ((LEAD + BODY) / 2) * MM + 4, mm(0.5), 'red', true),
  text('title', '{titleText}', face(SONG, 22, 900, 'ink'), lineTop(12)), // 二号, 2 lines under
] } };
const notice = { level: 1, span: 'page', advancedDesign: letterhead,
  marginTop: pt(0), marginBottom: pt(LEAD), // 空一行: a blank line, then the addressee
  breakBefore: { enabled: true, parity: 'any' } }; // gotcha: headings-drop-h1-break
// #endregion

// #region folios: “— 1 —” in 四号, 7 mm under the type area, a cell in from the outer edge
const FOLIO = 14; // pt: 四号
const folio = (id, parity, edge, x) => ({ kind: 'text', id, parity, content: '— {pageNumber} —',
  ...face(SONG, FOLIO, 400, 'ink', 1), align: edge.endsWith('left') ? 'left' : 'right',
  overflow: 'clip', placement: { anchor: { to: 'container', edge }, // the type area's foot
    offset: { x: pt(x), y: mm(7 - (FOLIO / 2) * MM) } } }); // the dashes 7 mm down
const footer = { elements: [folio('recto', 'odd', 'top-right', -FOLIO),
  folio('verso', 'even', 'top-left', FOLIO)] };
const header = { elements: [{ kind: 'text', id: 'specimen', content: '{subtitle}', // 样张 …
  ...face(HEI, 7.5, 400, 'muted', 1.2), align: 'center', overflow: 'wrap',
  placement: { anchor: { to: 'container', edge: 'top' }, offset: { y: mm(16) } } }] };
// #endregion

// #region annex: the annex on a page of its own, the 版记 at the foot of that last page
const IMPRINT = AREA.h - 2 * LINE; // mm: two rows of the grid, ending on the type area's foot
const small = face(SONG, FOLIO, 400, 'ink', LEAD / FOLIO); // 四号
const inset = { x: FOLIO * MM, width: AREA.w - 2 * FOLIO * MM, reserve: false }; // 左右各空一字
const annex = {
  id: 'annex', numbered: false, toc: false, breakBefore: { enabled: true, parity: 'any' },
  span: 'page', marginTop: pt(0), marginBottom: pt(0), // line 4 is the table's float gap
  advancedDesign: { enabled: true, minHeight: pt(3 * LEAD), slot: { elements: [
    text('label', '{attr.label}', face(HEI, BODY, 500, 'ink'), lineTop(1), { align: 'left' }),
    text('title', '{titleText}', face(SONG, 22, 900, 'ink'), lineTop(3)),
    // reserve: false keeps the 版记 out of the room the heading takes: the table goes on.
    rule('imprint-top', IMPRINT, mm(0.35)),
    text('cc', '抄送：{attr.cc}', small, IMPRINT, { ...inset, align: 'left' }),
    rule('imprint-mid', IMPRINT + LINE, mm(0.25)),
    text('office', '{attr.office}', small, IMPRINT + LINE, { ...inset, align: 'left' }),
    text('printed', '{attr.printed}', small, IMPRINT + LINE, { ...inset, align: 'right' }),
    rule('imprint-foot', AREA.h - 0.35 / 2, mm(0.35)),
    text('colophon', '{attr.colophon}', face(HEI, 7, 400, 'muted'), AREA.h + 16, inset),
  ] } },
};
// #endregion

// #region styles: the addressee flush left, the name and the date to the right
const paragraphStyles = [
  { id: 'flush', firstLineIndent: pt(0) }, // 主送机关：居左顶格
  { id: 'annexes', marginTop: pt(LEAD) }, // 附件说明：正文下空一行，左空二字
  // The date, 6.9 ems, starts two cells right of the name and ends two short: 右空二字.
  { id: 'signature', indent: em(17), firstLineIndent: pt(0), marginTop: pt(LEAD) },
  { id: 'date', indent: em(19), firstLineIndent: pt(0) },
];
// #endregion

// The annex's table: the days, the sessions and who teaches them, every cell centred.
const SCHEDULE = [['日期', '时间', '内容', '主讲'],
  ['10月20日', '上午9:00—11:30', '公文格式国家标准解读', '林　岚'],
  ['', '下午14:00—16:30', '版心、字体字号与行距', '周明远'],
  ['10月21日', '上午9:00—11:30', '标题层次、序数与页码', '陈思齐'],
  ['', '下午14:00—16:30', '书刊横排与竖排样张', '林　岚'],
  ['10月22日', '上午9:00—11:30', '公文样张排版实操', '周明远'],
  ['', '下午14:00—16:30', '上机考核与讲评', '全体教员']];
const cells = parseTSV(SCHEDULE.map((row) => row.join('\t')).join('\n')).rows
  .map((row) => row.map((c) => ({ ...c, align: 'center', verticalAlign: 'middle' })));
// Each date spans its two rows (gotcha: merged-cells-hiddenby). Widths in 四号 ems, 31.5 in all.
const schedule = [1, 3, 5].reduce((model, row) => mergeCells(model, { start: { row, col: 0 },
  end: { row: row + 1, col: 0 } }), { rows: cells, headerRowCount: 1,
  columnWidths: [5.6, 9.6, 11.3, 5] });
const resources = [{ id: 'schedule', typeId: 'schedule', kind: 'table', createdAt: 0,
  updatedAt: 0, placement: { position: 'here' }, table: { model: schedule } }];
const resourceTypes = [{ id: 'schedule', name: '日程', shortLabel: '', numberingTemplate: '',
  resetOn: 'never', counterFormat: 'decimal', captionPrefix: '' }]; // no label, no number

const config = () => ({ // a factory: the engine caches resolved configs per object
  locale: 'zh-Hans', // written out, never LANG (gotcha: cjk-locale-tag)
  colorPalette, page, layout: { layoutType: 'single' }, cjk, bodyText, resourceTypes,
  headings: { fontFamily: SONG, fontWeight: 400, color: col('ink'), levels: [notice, ...levels],
    balancing: { enabled: false } }, // no lines added over heads, no paragraph set loose
  headingStyles: [annex], paragraphStyles, header, footer,
  tableStyle: { borderColor: col('ink'), borderWidth: pt(0.75), cellPadding: mm(2),
    headerBackgroundEnabled: false, headerBold: false, headerFontFamily: HEI, bodyFontFamily: SONG,
    headerFontSize: pt(FOLIO), bodyFontSize: pt(FOLIO), // 四号
    headerColor: col('ink'), bodyColor: col('ink') },
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`---
نموذج Markdown · أسطر: 81 · content.en.md
title: "示例市出版协会关于举办2026年中文排版实务培训班的通知"
subtitle: "样张 · A specimen set to GB/T 9704—2012 · The association, its staff and this notice are fictitious"
---

# 示例市出版协会关于举办 \\ 2026年中文排版实务培训班的通知 {copy="000001" issuer="示例市出版协会" number="示出协〔2026〕7号"}

:::paragraphs{style="flush"}
各会员单位：
:::

为提高会员单位排版人员的业务水平，协会定于2026年10月举办中文排版实务培训班。现将有关事项通知如下：

## 培训时间

2026年10月20日至22日，共3天。参训人员于10月19日14:00至18:00到示例市图书大厦一楼大厅报到，报到时请出示单位介绍信。

## 培训地点

示例市图书大厦五楼报告厅（示例市文昌路88号）。

## 培训内容

### 排版规范

#### 公文格式

学习《党政机关公文格式》（GB/T 9704—2012），重点掌握以下两项内容：

##### 版心与字体

版心156毫米×225毫米，每页22行，每行28字，正文一般用3号仿宋体字。

##### 页码与版记

页码用4号半角阿拉伯数字，单页居右，双页居左；版记置于公文最后一页。

#### 标点符号

学习《标点符号用法》（GB/T 15834—2011），掌握标点在行首行末的禁则和两个标点连用时的处理。

### 实务操作

按字数和行数设定版心，完成书刊样张和公文样张各一份，由教员逐页讲评。

## 参加对象和名额

各会员单位从事编辑、校对和排版工作的人员，可自愿报名，每个单位限报2人，全市共80个名额，报满为止。

## 报名办法

报名时间为即日起至2026年10月10日，可任选以下一种方式报名。

### 网上报名

登录示例市出版协会网站“培训报名”栏目，填写报名表并上传近一年排版的书刊或公文一份。

### 书面报名

报名表加盖单位公章后，送至协会秘书处（示例市图书大厦十二楼）。

## 其他事项

培训不收取费用，食宿费用回原单位报销。参训人员须自带笔记本电脑。联系人：协会秘书处周明远、陈思齐。

:::paragraphs{style="annexes"}
附件：培训日程安排
:::

:::paragraphs{style="signature"}
示例市出版协会
:::

:::paragraphs{style="date"}
2026年9月28日
:::

（此件公开发布）

# 培训日程安排 {style="annex" label="附件" cc="示例市新闻出版局，示例市图书馆学会。" office="示例市出版协会秘书处" printed="2026年9月28日印发" colophon="Noto Serif SC, Noto Sans SC and LXGW WenKai TC (SIL OFL) · A fictitious notice written for the recipe"}

::resource{id="schedule"}
`; // content.<lang>.md, inlined by the Cookbook

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
const FONTS = { // every face the pages use, loaded before the build (gotcha: fonts-first)
  'Noto Serif SC': ['400', '900'], // SONG: the text, number, folios, 版记; the name, the titles
  'Noto Sans SC': ['400', '500'], // HEI: the head line, table heads; the 一、 heads, label, stamp
  'LXGW WenKai TC': ['400'], // KAI: the （一） heads
};

// ─── 4 · Build & show ───────────────────────────────────────────────────────
// Each voice loads the files of what it sets, template numerals too (gotcha: cjk-fonts-slices).
const lines = (re) => (markdown.match(re) ?? []).join('');
const [table, heads] = [SCHEDULE.flat().join(''), SCHEDULE[0].join('')];
await loadFonts(FONTS, markdown);
await loadCjkFonts({ [SONG]: ['400'] }, `${markdown}${table}0123456789—.（）`);
await loadCjkFonts({ [SONG]: ['900'] }, `${lines(/^# .*$/gm)}文件`);
await loadCjkFonts({ [HEI]: ['400'] }, `${lines(/^subtitle: .*$|colophon="[^"]*"/gm)}${heads}`);
await loadCjkFonts({ [HEI]: ['500'] }, `${lines(/^## .*$/gm)}一二三四五六七八九十、附件样　张`);
await loadCjkFonts({ [KAI]: ['400'] }, `${lines(/^### .*$/gm)}一二三四五六七八九十（）`);
const doc = await buildWithFonts(() => buildDocument({ markdown, resources }, config()), markdown);
showPages(doc, { title: t({ en: 'A Chinese official document to GB/T 9704',
  es: 'Un documento oficial chino según la GB/T 9704' }) });
offerPdf(() => renderToPdf(doc, { fontProvider: cjkPdfProvider }), `${RECIPE}.pdf`);

العُدّة · core, fonts, viewer, pdf, cjk: نفسها في كل وصفة · أسطر: 422
// ─── 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 v1 ── the same in every recipe · postext.dev/cookbook ────────
// Postext measures text with the faces the browser has loaded, and caches the
// widths, so every face must be ready before the first build. Faces come from
// Fontsource: the same static files the PDF embeds, so screen and PDF agree.

/** faces = { 'Family Name': ['400', '400i', '700'] }. `text` is the sample:
 *  letters beyond Latin-1 (č, ł, ő…) also load the latin-ext files. With
 *  `optional`, a face Fontsource does not ship is skipped instead of failing.
 *  Resolves to the number of faces added. */
async function loadFonts(faces, text = '', { optional = false } = {}) {
  kitStatus('Loading fonts…');
  const ranges = {
    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',
  };
  const subsets = /[Ā-˿Ḁ-ỿ]/.test(text) ? ['latin', 'latin-ext'] : ['latin'];
  const jobs = [];
  let added = 0;
  for (const [family, specs] of Object.entries(faces)) {
    const id = fontsourceId(family);
    const meta = optional ? await fontsourceMeta(family) : null;
    for (const spec of new Set(specs)) {
      const weight = parseInt(spec, 10);
      const style = spec.endsWith('i') ? 'italic' : 'normal';
      if (hasFace(family, weight, style)) continue;
      if (optional && !(meta?.weights.includes(weight) && meta.styles.includes(style))) continue;
      for (const subset of subsets) {
        const url = `https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-${subset}-${weight}-${style}.woff2`;
        const face = new FontFace(family, `url(${url}) format('woff2')`,
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        }));
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  await Promise.all(jobs).catch((error) => { kitFail(error); throw error; });
  return added;
}

/** Runs `build` (a buildDocument or buildBundle call) and checks the faces
 *  the pages use. A regular face missing from FONTS is loaded with a warning;
 *  bold and italic variants are loaded when the family ships them. Then the
 *  measurement caches are cleared and the build runs again. */
async function buildWithFonts(build, text = '') {
  const tried = new Set();
  for (let round = 0; round < 3; round++) {
    kitStatus('Laying out…');
    await new Promise(requestAnimationFrame);          // let the status paint first
    const result = await Promise.resolve().then(build).catch((error) => { kitFail(error); throw error; });
    const wanted = { base: {}, variants: {} };
    for (const { font, base } of [result].flat().flatMap(fontStringsOf)) {
      const { family, weight, style } = parseFont(font);
      const key = `${family}|${weight}|${style}`;
      if (tried.has(key) || hasFace(family, weight, style)) continue;
      tried.add(key);
      (wanted[base ? 'base' : 'variants'][family] ??= []).push(`${weight}${style === 'italic' ? 'i' : ''}`);
    }
    if (Object.keys(wanted.base).length) {
      console.warn(`[cookbook] FONTS does not list ${JSON.stringify(wanted.base)}: loading them.`);
    }
    const added = await loadFonts(wanted.base, text) + await loadFonts(wanted.variants, text, { optional: true });
    if (added === 0) return result;
    clearMeasurementCache();
  }
  throw new Error('The fonts did not settle after three builds.');
}

/** Every font string of the layout. `base` marks a block's own face; its
 *  bold, italic and bold-italic variants are listed whether or not used. */
function fontStringsOf(doc) {
  const found = new Map();
  const walk = (node) => {
    if (!node || typeof node !== 'object') return;
    if (Array.isArray(node)) { node.forEach(walk); return; }
    for (const [key, value] of Object.entries(node)) {
      if (typeof value === 'string' && /fontString$/i.test(key)) {
        found.set(value, found.get(value) || key === 'fontString');
      } else if (value && typeof value === 'object') walk(value);
    }
  };
  walk(doc.pages);
  walk(doc.blocks);
  return [...found].map(([font, base]) => ({ font, base }));
}

/** '700 37.5px Open Sans' / 'italic 400 13px "Source Serif 4"' → { family, weight, style }.
 *  A string with no weight ('95.8px Young Serif', from a design text) is 400. */
function parseFont(font) {
  const m = /^(?:(italic|oblique)\s+)?(?:small-caps\s+)?(?:(\d+|bold|normal)\s+)?[\d.]+px\s+(.+)$/.exec(font.trim());
  if (!m) throw new Error(`Unexpected font string: ${font}`);
  const weight = m[2] === 'bold' ? 700 : !m[2] || m[2] === 'normal' ? 400 : Number(m[2]);
  return { family: m[3].replace(/^["']|["']$/g, ''), weight, style: m[1] ? 'italic' : 'normal' };
}

/** True when a loaded FontFace covers exactly this family, weight and style
 *  (document.fonts.check() is also true 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;
}

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

/** The weights and styles a family ships ({ weights: [400, 700], styles: ['normal', 'italic'] }), 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 v1 ── the same in every recipe · postext.dev/cookbook ───────
/** Shows the pages as facing spreads on a dark desk: the first page is a
 *  recto on its own, then verso | recto pairs, as in a bound book. Pages
 *  are painted when they scroll near the screen. */
function showPages(docs, { title, width = 460 } = {}) {
  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, { 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 v1 ── the same in every recipe that exports a PDF ──────────────
/** postext-pdf embeds TrueType bytes. Fetch the Fontsource file the screen
 *  used, snapping to a weight the family ships and falling back to upright
 *  when it has no italic: the PDF asks for every face a block could use. */
async function fontsourceProvider(family, weight, style) {
  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 res = await fetch(`https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-latin-${w}-${s}.woff2`);
  if (!res.ok) throw new Error(`Fontsource has no ${family} ${w} ${s} (${res.status})`);
  return decompressWoff2(new Uint8Array(await res.arrayBuffer()));
}

/** A "Build the PDF" button in the bar. Once built: "Open the PDF" (a new
 *  tab, since CodePen's preview frame cannot show 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 · cjk v1 ── 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 = `https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/${weight}${style === 'italic' ? '-italic' : ''}.css`;
  if (!cjkSlices.cache.has(css)) {
    cjkSlices.cache.set(css, fetch(css)
      .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], css).href, range, ranges };
      }).reverse()));
  }
  return cjkSlices.cache.get(css);
}

/** The file of `slices` that holds code point `cp`, if any. */
function cjkSliceFor(slices, cp) {
  return slices.find((slice) => slice.ranges.some(([lo, hi]) => cp >= lo && cp <= hi));
}

/** 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 buildWithFonts 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 that
 *  hold the characters its pages set (`request.codePoints`); any other
 *  family goes to fontsourceProvider (the "pdf" block). */
async function cjkPdfProvider(family, weight, style, request) {
  if (!(await isCjkFamily(family))) return fontsourceProvider(family, weight, style);
  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.filter((slice) => picked.has(slice)).map(async (slice) => {
    const res = await fetch(slice.url);
    if (!res.ok) throw new Error(`Fontsource file ${slice.url} (${res.status})`);
    return decompressWoff2(new Uint8Array(await res.arrayBuffer()));
  }));
}

/** 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 ───────────────────────────────────────────────────────────────────────