专名号与书名号，竖排与横排

// ═══ Postext Cookbook · Nº 077 · Proper-name and book-title marks, across and down ═════
// https://postext.dev/en/cookbook/proper-name-marks
// Code: MIT · Text: Sima Qian, Shiji 7 (PD) · Punctuation, headnote, conventions: CC BY 4.0
// Fonts: Noto Serif TC, Noto Sans TC, LXGW WenKai TC (SIL OFL 1.1) · Needs postext ≥ 1.9.0
// Specimen pages for a classical reader: the opening of the Basic Annals of Xiang Yu with
// its proper-name lines and wavy title lines, set down the page and then across it.
import {
  buildDocument, renderPageToCanvas, clearMeasurementCache, loadVerticalAlternates,
} from 'https://esm.sh/postext';
import { renderToPdf, decompressWoff2 } from 'https://esm.sh/postext-pdf';

const LANG = 'en'; // @lang: the language of the slug lines and the colophon ('en' | 'es')
const RECIPE = 'proper-name-marks';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// #region palette: the indigo of a thread-bound cover, vermilion for the marks
const palette = {
  ink: '#221e1b', // the text
  band: '#23394b', // the opener band and the small heads
  mark: '#b5412c', // the name, title and emphasis marks: the second ink
  tint: '#c7d2da', // kickers and bylines on the band
  muted: '#6f6a64', // folios, slug lines, 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: 'band (defaults)', value: { hex: palette.band, model: 'hex' } },
];
// #endregion
// #region type: 五號 on 18 pt, 42 characters by 17 lines down the page
const [SONG, HEI, KAI] = ['Noto Serif TC', 'Noto Sans TC', 'LXGW WenKai TC']; // 宋, 黑, 楷
const PT = 25.4 / 72; // mm in a point
const [W, H] = [140, 203]; // mm: 大32開
const SIZE = 10.5; // pt: 五號
// A gap of 7.5 pt (0.71 em) between lines: a line of marks needs half an em of it, dots on
// one side and lines on the other five eighths. At 15 pt the build reports every marked
// paragraph (cjkMarksExceedLeading: gap 0.43 em).
const LEAD = 18; // pt
const [CHARS, LINES] = [42, 17]; // the vertical grid: characters down a line, lines across
const SIDE = (W - LINES * LEAD * PT) / 2; // mm: the side margins of a vertical page
// #endregion

// #region answer: marks by the markup, their side by the writing mode
// :name[項梁] draws the proper-name line, :book[史記] the book-title mark, :dots[…] dots.
const cjk = {
  bookTitleMark: 'wavy', // zh-Hant's default; mainland editions of the classics use it too
  annotationColor: col('mark'), // unset, the marks print in the colour of the text
  grid: { enabled: true, charsPerLine: CHARS, linesPerPage: LINES },
};
// The book runs down the page, bound on the right: the lines stand left of the names.
const layout = { layoutType: 'single', writingMode: 'vertical-rl' };
// # 項羽本紀 {style="across"} sets the same Markdown across the page, 28 characters to
// the line: the lines run under the names. Its margins set its grid; the book's grid
// counts down the page.
const MEASURE = 28 * SIZE * PT; // mm
const across = {
  id: 'across',
  layout: { layoutType: 'single', writingMode: 'horizontal-tb' },
  margins: { top: mm(SIDE), bottom: mm(H - SIDE - 25 * LEAD * PT), // 25 lines
    left: mm((W - MEASURE) / 2), right: mm((W - MEASURE) / 2) },
};
// #endregion

// #region opener: one design both ways: a band over the text across, right of it down
// The grid centres the text between the minimum margins; the band stops at its foot.
const FOOT = 20 + (H - 24 - 20 - CHARS * SIZE * PT) / 2; // mm, with minimums of 24 and 20
const BAND = SIDE + 3.5 * LEAD * PT; // mm from the trim, which is the right edge down the page
const onBand = { align: 'left', overflow: 'wrap' }; // design text centres and cuts by default
const next = (id, y) => ({ anchor: { to: `#${id}`, edge: 'below' }, offset: { y: mm(y) } });
const opener = {
  enabled: true,
  minHeight: pt(4 * LEAD), // the text starts on the fifth line, half a line clear of the band
  slot: { elements: [
    // Across the page the band's length runs past the trim; down it, it ends at the text's
    // foot, clear of the folio.
    { kind: 'box', id: 'band', style: { backgroundColor: col('band') },
      placement: { anchor: { to: 'bleed', edge: 'top-left' },
        size: { width: mm(H - FOOT), height: mm(BAND) } } },
    { kind: 'text', id: 'kicker', content: '{attr.kicker}', ...onBand, fontFamily: HEI,
      fontWeight: 700, fontSize: pt(8), letterSpacing: pt(1.6), color: col('tint'),
      placement: { anchor: { to: 'container', edge: 'top-left' }, offset: { y: mm(6 - SIDE) } } },
    { kind: 'text', id: 'title', content: '{titleText}', ...onBand, fontFamily: SONG,
      fontWeight: 700, fontSize: pt(46), lineHeight: 1, letterSpacing: pt(3),
      color: col('paper'), placement: next('kicker', 2) },
    { kind: 'text', id: 'byline', content: '{attr.byline}', ...onBand, fontFamily: KAI,
      fontSize: pt(10), color: col('tint'), placement: next('title', 2) },
  ] },
};
// #endregion

// #region folios: Chinese numerals at the outer foot, the slug line in the middle
const foot = (id, content, parity, edge, x, extra) => ({ kind: 'text', id, content, parity,
  fontFamily: HEI, fontSize: pt(7), color: col('muted'), ...extra,
  placement: { anchor: { to: 'page', edge }, offset: { x: mm(x), y: mm(-11) } } });
const folio = { fontFamily: SONG, fontSize: pt(9) };
// Bound on the right, a recto (odd) lies left of the spine: its outer edge is its left one.
const footer = { elements: [
  foot('folio-odd', '{pageNumber}', 'odd', 'bottom-left', SIDE, folio),
  foot('folio-even', '{pageNumber}', 'even', 'bottom-right', -SIDE, folio),
  foot('slug', '{attr.slug}', 'all', 'bottom', 0, { letterSpacing: pt(0.4) }),
] };
// #endregion

// The front page sets the headnote and the conventions in the Kai face. A section's
// bodyStyle sets its list numbers bold unless its orderedLists say otherwise.
const front = { id: 'front', bodyStyle: { fontFamily: KAI, orderedLists: { fontWeight: 400 } } };

const config = () => ({ // a factory: the engine caches resolved configs per object
  locale: 'zh-Hant', // Taiwan: full-width centred punctuation (gotcha: cjk-locale-tag)
  colorPalette,
  page: {
    sizePreset: 'custom', width: mm(W), height: mm(H), dpi: 150,
    // Minimums: the grid centres its 42 × 17 characters, 天頭 25.7 mm over 地腳 21.7 mm.
    margins: { top: mm(24), bottom: mm(20), left: mm(SIDE), right: mm(SIDE), mirror: true },
    pageNumbering: { format: 'trad-chinese-informal' }, // 一, 二, 三
  },
  layout,
  cjk,
  bodyText: {
    fontFamily: SONG, fontSize: pt(SIZE), lineHeight: pt(LEAD), color: col('ink'),
    boldColor: col('ink'), italicColor: col('ink'), referenceColor: col('ink'),
    textAlign: 'justify', firstLineIndent: em(2), indentAfterHeading: true,
  },
  headings: {
    fontFamily: HEI, fontWeight: 700, color: col('band'),
    levels: [
      // Restated: any headings object drops the H1 break (gotcha: headings-drop-h1-break).
      { level: 1, span: 'page', breakBefore: { enabled: true, parity: 'any' },
        advancedDesign: opener, marginBottom: pt(0) },
      // No space above: 題解 sits on the fifth line, where the other pages' text starts;
      // a :::space line sets 凡例 apart from the headnote.
      { level: 2, fontSize: pt(SIZE), lineHeight: pt(LEAD), letterSpacing: pt(2),
        marginTop: pt(0), marginBottom: pt(0) },
    ],
  },
  headingStyles: [front, across],
  // No gap after 一、: the text starts two ems in, on the grid, like a paragraph's.
  orderedLists: { numberFormat: 'trad-chinese-informal', separator: '、', fontFamily: KAI,
    fontWeight: 400, color: col('ink'), gap: em(0), marginTop: pt(0), marginBottom: pt(0) },
  paragraphStyles: [
    { id: 'colophon', fontFamily: HEI, fontSize: pt(7), lineHeight: pt(10), color: col('muted'),
      textAlign: 'left', firstLineIndent: pt(0), marginTop: pt(LEAD) },
  ],
  header: { elements: [] }, // every page opens a section: the band is its head
  footer,
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
// The Chinese is the same in both editions; the slug lines and the colophon change.
const markdown = String.raw`---
Markdown样例 · 43行 · content.en.md
title: "史記選讀"
author: "司馬遷"
---

# 史記選讀 {style="front" kicker="版式樣張" byline="題解　凡例" slug="Specimen sheet: the headnote and the conventions"}

## 題解

:book[項羽本紀]是:book[史記]第七卷，記述:name[秦]末:name[項羽]起兵、分封諸侯，以至兵敗:name[垓下]、自刎:name[烏江]的始末。:name[司馬遷]將這位未曾稱帝的人物列入「本紀」，與帝王並列。本樣張節錄篇首，寫:name[項羽]的出身與少年志氣。:name[東漢]:name[班固]:book[漢書]:book[陳勝項籍傳]敘述同一段事，文字大多沿用:book[史記]。

:::space

## 凡例

1. 正文依維基文庫所收:book[史記]卷七錄文；標點、分段與題解為本樣張所加。
2. 人名、地名、國名、朝代名旁加專名號，直排標於字左，橫排標於字下。
3. 書名、篇名旁加浪線書名號，位置與專名號相同，如:book[史記]:book[項羽本紀]。
4. 兩個專名緊相連接時各自畫線，相接處各縮八分之一字，如:name[楚]:name[漢]、:name[東漢]:name[班固]。
5. 需要強調的字旁加著重號，直排在字右，橫排在字下，如:dots[萬人敵]。

# 項羽本紀 {kicker="樣張一　直排" byline="〔漢〕司馬遷" slug="Specimen 1, down the page: the lines stand left of the names"}

:name[項籍]者，:name[下相]人也，字:name[羽]。初起時，年二十四。其季父:name[項梁]。:name[梁]父即:name[楚]將:name[項燕]，為:name[秦]將:name[王翦]所戮者也。:name[項氏]世世為:name[楚]將，封於:name[項]，故姓:name[項氏]。

:name[項籍]少時，學書不成，去學劍，又不成。:name[項梁]怒之。:name[籍]曰：「書，足以記名姓而已；劍，一人敵，不足學。學萬人敵。」於是:name[項梁]乃教:name[籍]兵法。:name[籍]大喜，略知其意，又不肯竟學。

:name[項梁]嘗有:name[櫟陽]逮，乃請:name[蘄]獄掾:name[曹咎]書抵:name[櫟陽]獄掾:name[司馬欣]，以故事得已。:name[項梁]殺人，與:name[籍]避仇於:name[吳中]，:name[吳中]賢士大夫皆出:name[項梁]下。每:name[吳中]有大繇役及喪，:name[項梁]常為主辦，陰以兵法部勒賓客及子弟，以是知其能。

:name[秦始皇帝]游:name[會稽]，渡:name[浙江]，:name[梁]與:name[籍]俱觀。:name[籍]曰：「彼可取而代也！」:name[梁]掩其口曰：「毋妄言，族矣。」:name[梁]以此奇:name[籍]。:name[籍]長八尺餘，力能扛鼎，才氣過人，雖:name[吳中]子弟，皆已憚:name[籍]矣。

# 項羽本紀 {style="across" kicker="樣張二　橫排" byline="〔漢〕司馬遷" slug="Specimen 2, across the page: the lines run under the names"}

:name[項籍]者，:name[下相]人也，字:name[羽]。初起時，年二十四。其季父:name[項梁]。:name[梁]父即:name[楚]將:name[項燕]，為:name[秦]將:name[王翦]所戮者也。:name[項氏]世世為:name[楚]將，封於:name[項]，故姓:name[項氏]。

:name[項籍]少時，學書不成，去學劍，又不成。:name[項梁]怒之。:name[籍]曰：「書，足以記名姓而已；劍，一人敵，不足學。學萬人敵。」於是:name[項梁]乃教:name[籍]兵法。:name[籍]大喜，略知其意，又不肯竟學。

:name[項梁]嘗有:name[櫟陽]逮，乃請:name[蘄]獄掾:name[曹咎]書抵:name[櫟陽]獄掾:name[司馬欣]，以故事得已。:name[項梁]殺人，與:name[籍]避仇於:name[吳中]，:name[吳中]賢士大夫皆出:name[項梁]下。每:name[吳中]有大繇役及喪，:name[項梁]常為主辦，陰以兵法部勒賓客及子弟，以是知其能。

:name[秦始皇帝]游:name[會稽]，渡:name[浙江]，:name[梁]與:name[籍]俱觀。:name[籍]曰：「彼可取而代也！」:name[梁]掩其口曰：「毋妄言，族矣。」:name[梁]以此奇:name[籍]。:name[籍]長八尺餘，力能扛鼎，才氣過人，雖:name[吳中]子弟，皆已憚:name[籍]矣。

:::paragraphs{style="colophon"}
Set in Noto Serif TC, Noto Sans TC and LXGW WenKai TC (SIL Open Font License). Text: Sima Qian, Shiji, chapter 7, from zh.wikisource (public domain). Punctuation, paragraphs, headnote and conventions written for this specimen (CC BY 4.0).
:::
`; // content.<lang>.md, inlined by the Cookbook

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
// A Chinese face comes in slices: each voice loads the files of the text it sets
// (gotcha: cjk-fonts-slices). Kai sets the front page and the bylines, Hei the small heads.
const FONTS = {
  'Noto Serif TC': ['400', '700'],
  'Noto Sans TC': ['400', '700'],
  'LXGW WenKai TC': ['400'],
};
const heads = markdown.match(/^#.*$/gm).join('\n'); // titles, kickers, bylines, slug lines
const preface = markdown.slice(0, markdown.indexOf('\n# ', markdown.indexOf('# ') + 2));
const colophon = markdown.slice(markdown.lastIndexOf(':::paragraphs'));
const NUMERALS = '一二三四五六七八九十、'; // folios and list numbers, which the text may lack

// ─── 4 · Build & show ───────────────────────────────────────────────────────
await loadFonts(FONTS, markdown);
await loadCjkFonts({ [SONG]: ['400'] }, markdown + NUMERALS, { vertical: true });
// The bold sets the two titles, which have no punctuation, so it loads no vertical forms.
// A browser that ignores the forms' feature settings would otherwise take a twin of the
// bold files for vertical forms and set the text's brackets upright in the regular.
await loadCjkFonts({ [SONG]: ['700'] }, heads);
await loadCjkFonts({ [HEI]: ['400', '700'] }, heads + colophon, { vertical: true });
await loadCjkFonts({ [KAI]: ['400'] }, preface + heads + NUMERALS, { vertical: true });
const doc = await buildWithFonts(() => buildDocument({ markdown }, config()), markdown);
showBook(doc, { title: t({ en: 'Name and title marks, down and across',
  es: 'Marcas de nombre y de título, en vertical y en horizontal' }) });
offerPdf(() => renderToPdf(doc, { fontProvider: cjkPdfProvider }), `${RECIPE}.pdf`);

工具包 · core, fonts, viewer, pdf, cjk：每道食谱都相同 · 422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 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')`,
          { weight: String(weight), style, unicodeRange: ranges[subset] });
        jobs.push(face.load().then((ready) => { document.fonts.add(ready); added++; }, () => {
          if (subset === 'latin' && !optional) throw new Error(`Fontsource has no ${family} ${weight} ${style}`);
        }));
      }
    }
  }
  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 ───────────────────────────────────────────────────────────────────────