Um artigo chinês citado pela GB/T 7714

// ═══ Postext Cookbook · Nº 090 · A Chinese paper cited to GB/T 7714 ═════════════════
// https://postext.dev/en/cookbook/gbt7714-chinese-paper
// Code: MIT · Text: original (CC BY 4.0) · Pictures: none
// Fonts: Noto Serif SC, Noto Sans SC, LXGW WenKai TC (SIL OFL 1.1) · Needs postext ≥ 1.12.0
import {
  buildDocument, renderPageToCanvas, clearMeasurementCache, registerCitationEngine,
} from 'https://esm.sh/postext';
import { renderToPdf, decompressWoff2 } from 'https://esm.sh/postext-pdf';
import { createCiteprocEngine, STYLES, LOCALES } from 'https://esm.sh/postext-citeproc';

const LANG = 'en'; // @lang: the language of the frame; the paper is Chinese in both editions
const RECIPE = 'gbt7714-chinese-paper';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// #region palette: black text, one indigo for the journal's name, its rules and its labels
const palette = {
  ink: '#1a1a1a', indigo: '#24427a', mist: '#b8c6e0', rule: '#9aa3b5', muted: '#5f6470',
  paper: '#ffffff',
};
const col = (id) => ({ hex: palette[id], model: 'hex', paletteId: id });
const colorPalette = Object.entries({ ...palette, 'main-color': palette.indigo })
  .map(([id, hex]) => ({ id, name: id, value: { hex, model: 'hex' } }));
// #endregion
const [SONG, HEI, KAI] = ['Noto Serif SC', 'Noto Sans SC', 'LXGW WenKai TC']; // 宋, 黑, 楷
const [BODY, LEAD] = [9, 15]; // pt: 小五 on a 15 pt line, the grid both columns share
const [CHARS, LINES] = [23, 40]; // characters to a column's line, lines to a column
const PT = 25.4 / 72; // mm in a point
const AREA = (2 * CHARS + 2) * BODY * PT; // mm: two columns and a 2-em gutter, 152.4

// #region answer: GB/T 7714 numbered: [1] in citation order, [2–4], 等 or et al. by language
// Register the engine once, before the first build. The GB/T 7714 numeric style writes
// superscript [n] in the order works are first cited, joins three or more in a row into a
// range and sets the list with its type codes: [M] book, [J] article, [D] thesis, [C]
// conference paper, [EB/OL] web page. Its CSL file holds a second layout for works whose
// language is English, with "et al." for 等, commented out: uncommented, a Western entry
// takes "et al." and a Chinese one keeps 等, each chosen by the entry's `language`.
registerCitationEngine(createCiteprocEngine({ styles: STYLES, locales: LOCALES }));
const GBT = STYLES['china-national-standard-gb-t-7714-2015-numeric'];
const citations = {
  style: 'custom', // the bundled style with its English layout switched on
  customStyle: GBT.replace(/<!-- (<layout[^>]*locale="en">[\s\S]*?<\/layout>)\s*-->/, '$1'),
  locale: 'zh-CN', // 等, 卷, 版 and the other terms of the list
  bibliography: { fontSize: em(7.5 / BODY), lineHeight: pt(12), entrySpacing: pt(1.5),
    labelWidth: em(1.7) }, // turnovers under the text, not past it: [1] and a space
};
// #endregion

// #region masthead: the journal's name on an indigo band, then title, authors, affiliations
const BAND = 30; // mm from the trim's top
const at = (id, edge, y) => ({ anchor: { to: id ? `#${id}` : 'container', edge },
  offset: { y: mm(y) }, size: { width: mm(AREA) } });
const line = (id, content, family, size, color, placement, extra) => ({ kind: 'text', id,
  content, fontFamily: family, fontSize: pt(size), color: col(color), align: 'center',
  overflow: 'wrap', placement, ...extra });
const onBand = (x, y) => ({ anchor: { to: 'page', edge: 'top-left' },
  offset: { x: mm(x), y: mm(y) }, size: { width: mm(AREA) } });
const masthead = { enabled: true, minHeight: pt(9 * LEAD), slot: { elements: [
  { kind: 'box', id: 'band', style: { backgroundColor: col('indigo') },
    placement: { anchor: { to: 'page', edge: 'top-left' },
      size: { width: 'fill', height: mm(BAND) } } },
  line('journal', '示例出版研究', HEI, 15, 'paper', onBand(15.8, 13),
    { fontWeight: 700, align: 'left', letterSpacing: pt(3) }),
  line('issue', '第44卷　第3期　2026年9月', HEI, 8, 'mist', onBand(15.8, 16),
    { align: 'right' }),
  line('title', '{titleText}', HEI, 17, 'ink', at('', 'top-left', 14),
    { fontWeight: 700, lineHeight: 1.45 }),
  line('authors', '{attr.authors}', KAI, 12, 'ink', at('title', 'below', 4)),
  line('affiliations', '{attr.affiliations}', SONG, 7.5, 'muted', at('authors', 'below', 2)),
] } };
// #endregion

// #region abstract: across both columns, its labels in 黑 the colour of the journal
// In 宋, not 楷: the one Kai on Fontsource is a Taiwan face (gotcha: cjk-face-region).
const calloutStyles = [{ id: 'abstract', span: 'page', backgroundEnabled: false,
  padding: { top: pt(0), bottom: pt(0), left: em(2), right: em(2) },
  marginTop: pt(0), marginBottom: pt(LEAD),
  body: { fontFamily: SONG, fontSize: pt(BODY), lineHeight: pt(LEAD), firstLineIndent: pt(0),
    textAlign: 'justify' } }];
const chipStyles = [{ id: 'label', fontFamily: HEI, bold: true, color: col('indigo'),
  backgroundEnabled: false, borderWidth: pt(0), paddingX: em(0), gap: em(0.5) }];
// #endregion

// Running heads on the body pages, the folio at the outer corner, over a hairline.
const head = (id, content, parity, edge, x, extra) => ({ kind: 'text', id, content, parity,
  pages: 'body', fontFamily: HEI, fontSize: pt(7.5), color: col('muted'), overflow: 'clip',
  align: edge, placement: { anchor: { to: 'page', edge: `top-${edge}` },
    offset: { x: mm(x), y: mm(12) } }, ...extra });
const folio = { fontWeight: 700, color: col('indigo') };
const header = { elements: [
  head('v-folio', '{pageNumber}', 'even', 'left', 15.8, folio),
  head('v-head', '示例出版研究　2026年第3期', 'even', 'left', 24),
  head('r-head', '赵一鸣，等：横排中文正文的行长与行距', 'odd', 'right', -24),
  head('r-folio', '{pageNumber}', 'odd', 'right', -15.8, folio),
  { kind: 'rule', id: 'head-rule', pages: 'body', thickness: pt(0.5), color: col('rule'),
    placement: { anchor: { to: 'page', edge: 'top-left' }, offset: { x: mm(15.8), y: mm(16.5) },
      size: { width: mm(AREA) } } },
] };

const config = () => ({ // a factory: the engine caches resolved configs per object
  locale: 'zh-Hans', // written out, never LANG (gotcha: cjk-locale-tag)
  colorPalette,
  citations,
  page: { width: mm(184), height: mm(260), dpi: 150, pageNumbering: { startAt: 41 },
    // 16开; with the grid on the margins are minimums, grown to centre the 23 × 40 area
    margins: { top: mm(22), bottom: mm(20), left: mm(15), right: mm(15), mirror: true } },
  layout: { layoutType: 'double', gutterWidth: pt(2 * BODY) },
  cjk: { grid: { enabled: true, charsPerLine: CHARS, linesPerPage: LINES } },
  bodyText: {
    fontFamily: SONG, fontSize: pt(BODY), 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('ink'),
    balancing: { enabled: false }, // heads stay on the grid
    levels: [
      { level: 1, breakBefore: { enabled: true, parity: 'any' } }, // headings-drop-h1-break
      { level: 2, numberingTemplate: '{2}', numberSeparator: '　', fontSize: pt(10.5),
        lineHeight: pt(2 * LEAD), marginTop: pt(0), marginBottom: pt(0) }, // 1　实验方法
      { level: 3, numberingTemplate: '{2}.{3}', numberSeparator: '　', fontSize: pt(BODY),
        lineHeight: pt(LEAD), marginTop: pt(0), marginBottom: pt(0) }, // 1.1　被试
    ] },
  headingStyles: [
    { id: 'article', numbered: false, span: 'page', advancedDesign: masthead },
    { id: 'intro', numbered: false }, // 引言 goes before section 1, unnumbered
    { id: 'references', numbered: false },
  ],
  calloutStyles,
  chipStyles,
  paragraphStyles: [{ id: 'colophon', fontFamily: SONG, fontSize: pt(6.5), lineHeight: pt(9),
    color: col('muted'), firstLineIndent: pt(0), textAlign: 'left', marginTop: pt(LEAD) }],
  header,
  footer: { elements: [] },
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`---
Amostra em Markdown · 140 linhas · content.en.md
title: "横排中文正文的行长与行距"
---

# 横排中文正文的行长与行距：\\一项纸本与屏幕的对照阅读实验 {style="article" authors="赵一鸣¹　孙雨桐²" affiliations="1. 示例大学新闻与传播学院，示例市　100000；2. 示例出版社排版中心，示例市　100000"}

:::callout{type="abstract"}
:chip[摘　要：]{style="label"}行长和行距是横排中文正文最基本的两个版式参数，现行出版物大多凭经验确定。本文以48名大学生为被试，比较每行20、28、36字三种行长与1.5倍、1.8倍两种行距在纸本和屏幕上的阅读速度与理解成绩。结果表明：行长为28字时阅读速度最快；行长增至36字，纸本上的理解成绩无显著变化，屏幕上则下降约6%；1.8倍行距的优势在长行条件下比在短行条件下明显。据此建议单栏横排书刊正文以每行26～30字为宜，行长超过32字时应相应加大行距。

:chip[关键词：]{style="label"}行长；行距；中文排版；阅读速度；屏幕阅读

:chip[文献标志码：]{style="label"}A　　:chip[文章编号：]{style="label"}1000-0000(2026)03-0041-04
:::

## 引言 {style="intro"}

行长与行距对阅读的影响，西文排版界讨论已久。Tinker在20世纪中叶以印刷品为材料做了大量易读性实验，认为最适宜的行长取决于字号和行距，不能脱离二者单独规定[@tinker1963]。近二十年来，眼动记录和屏幕阅读进入这一领域，研究者发现阅读速度与理解成绩并不总是同步变化，只用速度评价版式容易得出片面的结论[@rayner2016; @dyson2001; @lin2023]。

中文的情况与西文不同。汉字等宽，行长可以直接用字数计量，出版社也习惯以“每行字数×每页行数”规定版心，32开图书的正文多为每行26～28字[@zhou2019; @chen2021]。W3C的《中文排版需求》整理了中文版面的基本要素和术语[@clreq]，但行长、行距取什么值，仍由各出版社自行决定。

这些数值大多来自排版经验，以汉字为材料、同时比较纸本与屏幕的实证研究还很少。林岚等[@lin2023]测量了屏幕上三种行长的阅读速度，没有考察行距；王晓和李文[@wang2022]讨论了屏幕阅读中的行距，只用了一种行长。本研究把行长和行距放在同一个实验中，在纸本和屏幕上分别测量阅读速度和理解成绩，为书刊正文的版式设计提供依据。

## 实验方法

### 被试

示例大学本科生48名，其中男生21名、女生27名，年龄18～23岁，母语均为汉语，视力或矫正视力正常，此前均未参加过阅读实验。

### 材料与版式

从近年出版的科普读物中选取说明文24篇，每篇约600字，难度经预实验平衡。版式按3（行长：每行20、28、36字）×2（行距：1.5倍、1.8倍）设计，字号统一为五号（10.5 pt），字体为宋体，两端对齐。纸本材料用A4纸单面印刷；屏幕材料在27英寸显示器上呈现，调整显示比例，使字的视角大小与纸本一致。

### 程序与测量

每名被试在纸本和屏幕上各读12篇，媒介的先后顺序在被试间平衡，版式条件在篇目间轮换。每读完一篇，回答5道理解题。阅读速度以每分钟字数计，理解成绩以答对题数的百分比计。屏幕条件下同时记录眼动，采样率为1000 Hz。

## 结果

### 阅读速度

行长为28字时，纸本和屏幕上的阅读速度均为最快，平均每分钟分别读512字和486字。行长20字时，换行次数增多，速度下降4%左右；行长36字时，速度下降7%左右，眼动记录显示换行后的回视次数明显增加。行太短和太长都会降低速度，这与Tinker对西文的观察方向一致[@tinker1963]。

### 理解成绩

纸本上，三种行长的理解成绩差异不显著。屏幕上，行长36字时的理解成绩比28字时低约6%。行距的作用主要出现在长行条件下：行长36字时，1.8倍行距的理解成绩比1.5倍行距高约4%；行长20字时，两种行距几乎没有差别。

## 讨论

长行降低了屏幕阅读的理解成绩，原因可能在换行时的视线定位。行越长，眼睛从行尾回到下一行行首的距离越大，落点越容易偏离；加大行距，相邻两行分得更开，这类错误随之减少。这一解释与眼动研究对换行和回视的描述相符[@rayner2016]，也说明行长和行距需要一并考虑。

本研究的材料只有说明文，被试也限于大学生；文学作品和其他年龄段的读者是否表现出同样的规律，还需要进一步检验。屏幕条件只用了一种显示器，没有考察手机等小屏幕设备，那里的行长通常不到20字。

## 结论

单栏横排的中文书刊正文，每行26～30字是较稳妥的选择。行长超过32字时，行距宜加大到1.8倍左右。面向屏幕的版式比纸本更需要控制行长，不宜把纸本的版心原样搬到屏幕上。

## 参考文献 {style="references"}

:::bibliography{title=""}

:::paragraphs{style="colophon"}
A specimen article written for the Postext Cookbook. The journal, its authors, their experiment and the Chinese works [4]–[6] and [8] are fictitious; works [1]–[3] and [7] are real.
:::

:::references{format=csl-yaml}
- id: tinker1963
  type: book
  language: en
  author: [{family: Tinker, given: Miles A.}]
  title: Legibility of print
  publisher: Iowa State University Press
  publisher-place: Ames
  issued: 1963
- id: rayner2016
  type: article-journal
  language: en
  author: [{family: Rayner, given: Keith}, {family: Schotter, given: Elizabeth R.}, {family: Masson, given: Michael E. J.}, {family: Potter, given: Mary C.}, {family: Treiman, given: Rebecca}]
  title: "So much to read, so little time: how do we read, and can speed reading help?"
  container-title: Psychological Science in the Public Interest
  volume: 17
  issue: 1
  page: 4-34
  issued: 2016
  DOI: 10.1177/1529100615623267
- id: dyson2001
  type: article-journal
  language: en
  author: [{family: Dyson, given: Mary C.}, {family: Haselgrove, given: Mark}]
  title: The influence of reading speed and line length on the effectiveness of reading from screen
  container-title: International Journal of Human-Computer Studies
  volume: 54
  issue: 4
  page: 585-612
  issued: 2001
  DOI: 10.1006/ijhc.2001.0458
- id: lin2023
  type: article-journal
  language: zh-CN
  author: [{literal: 林岚}, {literal: 周明远}, {literal: 陈思齐}, {literal: 王晓}]
  title: 屏幕上横排中文的行长与阅读速度
  container-title: 示例出版研究
  volume: 41
  issue: 2
  page: 15-24
  issued: 2023
- id: zhou2019
  type: book
  language: zh-CN
  author: [{literal: 周明远}]
  title: 汉字排版概论
  publisher: 示例出版社
  publisher-place: 示例市
  issued: 2019
- id: chen2021
  type: thesis
  genre: 硕士学位论文
  language: zh-CN
  author: [{literal: 陈思齐}]
  title: 中文书刊版心设计研究
  publisher: 示例大学
  publisher-place: 示例市
  issued: 2021
- id: wang2022
  type: paper-conference
  language: zh-CN
  author: [{literal: 王晓}, {literal: 李文}]
  title: 屏幕阅读中的行距选择
  container-title: 第五届数字出版学术研讨会论文集
  editor: [{literal: 示例出版学会}]
  publisher: 示例出版社
  publisher-place: 示例市
  page: 88-95
  issued: 2022
- id: clreq
  type: webpage
  language: zh-CN
  author: [{literal: W3C}]
  title: 中文排版需求
  URL: https://www.w3.org/TR/clreq/
  accessed: 2026-09-30
:::
`; // content.<lang>.md: the same Chinese text in both

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
const FONTS = { // every face the pages use, loaded before the build (gotcha: fonts-first)
  'Noto Serif SC': ['400'], // SONG: the text, the references, the affiliations
  'Noto Sans SC': ['400', '700'], // HEI: running heads; the journal, title, heads, labels
  'LXGW WenKai TC': ['400'], // KAI: the authors' names
};

// ─── 4 · Build & show ───────────────────────────────────────────────────────
// Each voice loads the files of what it sets, and the Song the words the style adds.
const all = (re) => (markdown.match(re) ?? []).join('');
const labels = all(/:chip\[[^\]]*\]/g);
const heads = `${all(/^#+ .*$/gm)}示例出版研究第卷期年月赵一鸣等横排中文正文的行长与行距`;
await loadFonts(FONTS, markdown);
await loadCjkFonts({ [SONG]: ['400'] }, `${markdown}等版卷期页`);
await loadCjkFonts({ [HEI]: ['400', '700'] }, `${heads}${labels}0123456789`);
await loadCjkFonts({ [KAI]: ['400'] }, all(/authors="[^"]*"/g));
const doc = await buildWithFonts(() => buildDocument({ markdown }, config()), markdown);
showPages(doc, { title: t({ en: 'A Chinese paper cited to GB/T 7714',
  es: 'Un artículo chino citado según la GB/T 7714' }) });
offerPdf(() => renderToPdf(doc, { fontProvider: cjkPdfProvider }), `${RECIPE}.pdf`);

Kit · core, fonts, viewer, pdf, cjk: igual em todas as receitas · 459 linhas
// ─── 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 v2 ── the same in every recipe · postext.dev/cookbook
// Postext measures with the loaded faces and caches the widths: load every face
// before the first build, from Fontsource, the files the PDF embeds too.

/** faces = { 'Family Name': ['400', '400i', '700'] }. `text` is the sample:
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    greek: 'U+0370-03FF',
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  const jobs = [];
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    const subsets = ['latin', ...kitSubsetsFor(text, meta)];
    for (const [weight, style] of todo) {
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  await Promise.all(jobs).catch((error) => { kitFail(error); throw error; });
  return added;
}

/** Runs `build` and loads any face the pages use that FONTS missed (a regular
 *  one with a warning), then clears the measurement cache and builds 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. */
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' };
}

/** 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, '-'); }

/** 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 v1 ── 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. */
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 v2 ── the same in every recipe that exports a PDF
/** The Fontsource files the screen used, as TrueType: the nearest weight the
 *  family ships, upright if it has no italic; latin, then what the face's
 *  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 more = kitSubsetsFor(text, meta);
  const files = await Promise.all(['latin', ...more].map(async (subset) => {
    const res = await fetch(`https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${id}-${subset}-${w}-${s}.woff2`);
    if (!res.ok) throw new Error(`Fontsource has no ${family} ${w} ${s} ${subset}`);
    return decompressWoff2(new Uint8Array(await res.arrayBuffer()));
  }));
  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 · 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 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.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()));
  }));
}

/** 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. Latin comes first: postext-pdf draws a character from the first
 *  file that has it, as the browser takes a character both files hold from
 *  latin. 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 = `https://cdn.jsdelivr.net/npm/@fontsource/${id}@5/files/${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)]);
  return ext ? [latin, ext] : 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 ───────────────────────────────────────────────────────────────────────