A vertical Chinese novel, bound on the right

// ═══ Postext Cookbook · Nº 075 · A vertical Chinese novel, bound on the right ════════
// https://postext.dev/en/cookbook/vertical-novel-right-bound
// Code: MIT · Text: 三國演義 ch. 1, zh.wikisource (CC BY-SA 4.0) · Plate: woodcut, 1592 (PD)
// Fonts: Noto Serif TC, LXGW WenKai TC, Noto Sans TC, Source Serif 4 (OFL) · Needs postext ≥ 1.9.0
import {
  buildDocument, renderPageToCanvas, clearMeasurementCache, registerResourceImage,
  loadVerticalAlternates,
} from 'https://esm.sh/postext';
import { renderToPdf, decompressWoff2 } from 'https://esm.sh/postext-pdf';

const LANG = 'en'; // @lang: the language of the frame; the novel is Chinese in both editions
const RECIPE = 'vertical-novel-right-bound';

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// #region palette: black ink, one vermilion, the paper the plate was toned to
const palette = {
  ink: '#2a221d', // the text, and the woodcut's lines
  vermilion: '#a3301f', // 朱: the ruled columns of the opener, the title slip
  muted: '#6f655c', // fore-edge heads, folios, the imprint
  paper: '#fbf8f1', // the page; the plate's paper was toned to this value
};
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: 'defaults', value: { hex: palette.vermilion, model: 'hex' } },
];
// #endregion
const [SONG, KAI, HEI] = ['Noto Serif TC', 'LXGW WenKai TC', 'Noto Sans TC']; // 宋, 楷, 黑
const ROMAN = 'Source Serif 4'; // the imprint: Noto Serif TC has no italic
const [BODY, LEAD] = [10.5, 19]; // pt: 五號 text on a column pitch of 1.8 em
const cols = (n) => pt(n * LEAD); // n columns across the page
const PT = 25.4 / 72; // mm in a point

// #region answer: vertical text on a 25開 page, bound on the right, 40 characters × 16 columns
// 'vertical-rl' turns the flow a quarter turn: lines run down, columns from right to left,
// and page.binding 'auto' becomes 'right', so page 1 is a left-hand page and the spreads
// read [3 | 2]. The grid sets the type area in characters; the margins are minimums it
// grows. zh-Hant resolves to Taiwan's rules: every mark full width and centred in its cell.
const page = {
  sizePreset: 'custom', width: mm(148), height: mm(210), dpi: 150,
  backgroundColor: col('paper'),
  // 天頭 above 地腳; left is the spine side (the right edge of a left-hand page).
  margins: { top: mm(32), bottom: mm(26), left: mm(16), right: mm(22), mirror: true },
  pageNumbering: { format: 'trad-chinese-informal' }, // folios 一, 二 … 九, from the chapter
};
const layout = { layoutType: 'single', writingMode: 'vertical-rl' };
const cjk = { grid: { enabled: true, charsPerLine: 40, linesPerPage: 16 } };
const chapter = {
  level: 1, numberingTemplate: '第{1:一}回', numberSeparator: '　', // 第一回　宴桃園…
  breakBefore: { enabled: true, parity: 'odd' }, // gotcha: headings-drop-h1-break
  marginBottom: pt(0),
};
// #endregion

// #region opener: 第一回 and the couplet in two ruled columns, a quotation of the woodblock
// In the flow frame x runs down the column and y across the page, right to left, so a
// 'horizontal' rule is a vertical line on the sheet: three of them rule the title columns.
const [TITLE, PITCH] = [13.5, 1.5 * LEAD]; // pt: the couplet's size and its column pitch
const rule = (n) => ({ kind: 'rule', id: `rule-${n}`, direction: 'horizontal',
  thickness: pt(0.5), color: col('vermilion'),
  placement: { anchor: { to: 'container', edge: 'top-left' },
    offset: { y: pt(LEAD + n * PITCH) }, size: { width: 'fill' } } });
const title = (id, content, x, family, weight) => ({ kind: 'text', id, content,
  fontFamily: family, fontWeight: weight, fontSize: pt(TITLE), lineHeight: PITCH / TITLE,
  color: col('ink'), align: 'left', // the head of the column
  placement: { anchor: { to: 'container', edge: 'top-left' },
    offset: { x: pt(x), y: pt(LEAD) } } }); // a line of PITCH, centred between two rules
const opener = {
  enabled: true,
  minHeight: cols(5), // a blank column, the two title columns, a blank one: 5 × 19 pt
  slot: { elements: [
    rule(0), rule(1), rule(2),
    title('number', '{number}', 2 * BODY, SONG, 700), // 第一回, two characters down
    // The couplet's two halves, broken by the \\ in the heading, start level with each other.
    title('couplet', '{titleText}', 2 * BODY + 4 * TITLE, KAI, 400),
  ] },
};
// #endregion

// #region fore-edge: the running head and the folio down the outer margin, in 黑
const foreEdge = (id, content, parity, edge, y, pages) => ({
  kind: 'text', id, content, parity, pages, writingMode: 'vertical-rl',
  fontFamily: HEI, fontSize: pt(8.5), color: col('muted'), overflow: 'clip',
  placement: { anchor: { to: 'outer', edge }, offset: { y: em(y) } },
});
const header = { elements: [
  foreEdge('book', '{title}', 'even', 'top', 4, 'body'), // 三國演義 on the right-hand page
  foreEdge('chapter', '{chapterNumber}　{chapterTitle}', 'odd', 'top', 4, 'body'),
  foreEdge('folio', '{pageNumber}', 'all', 'bottom', -5, 'all'), // on openers too
] };
// #endregion

// #region front: a title page and the plate facing the opener, no heads or folios
const none = { elements: [] };
// A point of a page design in the flow frame: mm down the column, mm leftward across the
// page from the right edge of the type area.
const at = (down, across) => ({ anchor: { to: 'container', edge: 'top-left' },
  offset: { x: mm(down), y: mm(across) } });
// The title slip (題簽), 96 × 22 mm: its axis, 55 mm in from the right of the type area, is
// the axis of the page, and of the imprint under it.
const SLIP = { down: 10, across: 44, long: 96, wide: 22 };
const AXIS = SLIP.across + SLIP.wide / 2;
const slip = (id, inset, thickness) => ({ kind: 'box', id,
  placement: { ...at(SLIP.down + inset, SLIP.across + inset),
    size: { width: mm(SLIP.long - 2 * inset), height: mm(SLIP.wide - 2 * inset) } },
  style: { borderColor: col('vermilion'), borderWidth: pt(thickness) } });
const RUN = (4 * 40 + 3 * 10) * PT; // 三國演義 down the slip: four 40 pt characters, 3 gaps
const titlePage = {
  id: 'title', numbered: false, toc: false, span: 'page', header: none,
  breakBefore: { enabled: true, parity: 'any' },
  footer: { elements: [{ kind: 'text', id: 'imprint', content: '{attr.colophon}',
    fontFamily: ROMAN, fontSize: pt(6.5), lineHeight: 1.4, color: col('muted'),
    // In the edition's language, set across and centred on the axis: the box runs from the
    // left of the type area (16 columns) as far past the axis. Each \n in the attribute
    // starts a line, and *…* sets the book's title in italic.
    inlineMarks: true, overflow: 'wrap', align: 'center',
    placement: { anchor: { to: 'container', edge: 'top-left' }, offset: { y: mm(4) },
      size: { width: mm(2 * (16 * LEAD * PT - AXIS)) } } }] },
  advancedDesign: { enabled: true, minHeight: cols(16), slot: { elements: [
    slip('slip', 0, 1.4), slip('slip-in', 1.2, 0.4), // a heavy and a light vermilion rule
    { kind: 'text', id: 'book', content: '{titleText}', fontFamily: SONG, fontWeight: 700,
      fontSize: pt(40), lineHeight: 1, letterSpacing: pt(10), color: col('ink'),
      placement: at(SLIP.down + (SLIP.long - RUN) / 2, AXIS - 20 * PT) }, // 40 pt line on the axis
    { kind: 'text', id: 'author', content: '{author}　著', fontFamily: KAI, fontSize: pt(12),
      color: col('ink'), placement: at(52, 72) },
    { kind: 'text', id: 'editor', content: '{attr.editor}', fontFamily: KAI, fontSize: pt(12),
      color: col('ink'), placement: at(52, 80) },
  ] } },
};
// The woodcut, 138 mm tall in a double frame (四周雙邊), hangs from the top right corner of
// the type area, and its caption runs down the column on its left. In the flow frame a
// box's width runs down the page: the picture's width is its height on the sheet, and it
// stands upright in the canvas, the HTML and the PDF.
const PLATE = { right: 8.3, top: 5.1, h: 138, w: (138 * 806) / 1427 }; // mm
const frame = (id, inset, thickness) => ({ kind: 'box', id,
  placement: { ...at(PLATE.top - inset, PLATE.right - inset),
    size: { width: mm(PLATE.h + 2 * inset), height: mm(PLATE.w + 2 * inset) } },
  style: { borderColor: col('ink'), borderWidth: pt(thickness) } });
const plate = {
  id: 'plate', numbered: false, toc: false, span: 'page', header: none, footer: none,
  breakBefore: { enabled: true, parity: 'any' },
  advancedDesign: { enabled: true, minHeight: cols(16), slot: { elements: [
    { kind: 'image', id: 'woodcut', resourceId: 'peach-garden',
      placement: { ...at(PLATE.top, PLATE.right), size: { width: mm(PLATE.h), height: 'auto' } } },
    frame('inner', 1.6, 0.4), frame('outer', 2.8, 1.4),
    { kind: 'text', id: 'caption', content: '{titleText}', fontFamily: HEI, fontSize: pt(9),
      color: col('ink'), placement: at(PLATE.top - 2.8, PLATE.right + PLATE.w + 7) },
    { kind: 'text', id: 'note', content: '{attr.note}', fontFamily: KAI, fontSize: pt(8),
      color: col('muted'), placement: at(PLATE.top - 2.8, PLATE.right + PLATE.w + 12) },
  ] } },
};
const resources = [{
  id: 'peach-garden', typeId: 'figure', kind: 'bitmap', createdAt: 0, updatedAt: 0,
  bitmap: { fileId: 'peach-garden.jpg', format: 'jpeg', width: 806, height: 1427 },
  caption: '桃園結義',
  altText: '桃園結義圖：劉備、關羽、張飛立於祭桌前，桌上香爐燭臺與三杯酒，旁有烏牛白馬。',
}];
// #endregion

const config = () => ({ // a factory: the engine caches resolved configs per object
  locale: 'zh-Hant', // written out, never LANG (gotcha: cjk-locale-tag)
  colorPalette,
  page,
  layout,
  cjk,
  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, // every paragraph
  },
  headings: { fontFamily: SONG, fontWeight: 700, color: col('ink'),
    levels: [{ ...chapter, advancedDesign: opener }] },
  headingStyles: [titlePage, plate],
  paragraphStyles: [
    // 詞 and 詩: one line to a column, four characters down, in 楷.
    { id: 'verse', fontFamily: KAI, textAlign: 'left', indent: em(4), firstLineIndent: em(0),
      marginTop: pt(0), marginBottom: pt(0) },
  ],
  header,
  footer: none,
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`---
Markdown sample · 69 lines · content.en.md
title: "三國演義"
author: "羅貫中"
---

# 三國演義 {style="title" editor="毛宗崗　評" colophon="Luo Guanzhong, *Romance of the Three Kingdoms*, chapter 1,\nin the recension of Mao Zonggang (about 1679).\nText: Chinese Wikisource, revision 2583915, CC BY-SA 4.0; one character corrected.\nPlate: woodcut from the edition of Yu Xiangdou, 1592.\nSet in Noto Serif TC, LXGW WenKai TC, Noto Sans TC and Source Serif 4 (SIL OFL)."}

# 桃園結義 {style="plate" note="明萬曆二十年余象斗刊《三國志傳評林》插圖"}

:::numbering{startAt=1}

# 宴桃園豪傑三結義 \\ 斬黃巾英雄首立功

詞曰：

:::paragraphs{style="verse"}
滾滾長江東逝水，浪花淘盡英雄。

是非成敗轉頭空：青山依舊在，幾度夕陽紅。

白髮漁樵江渚上，慣看秋月春風。

一壺濁酒喜相逢：古今多少事，都付笑談中。
:::

話說天下大勢，分久必合，合久必分。周末七國分爭，併入於秦。及秦滅之後，楚、漢分爭，又併入於漢。漢朝自高祖斬白蛇而起義，一統天下。後來光武中興，傳至獻帝，遂分為三國。推其致亂之由，殆始於桓、靈二帝。桓帝禁錮善類，崇信宦官。及桓帝崩，靈帝即位，大將軍竇武、太傅陳蕃，共相輔佐。時有宦官曹節等弄權，竇武、陳蕃謀誅之，作事不密，反為所害，中涓自此愈橫。

建寧二年四月望日，帝御溫德殿。方陞座，殿角狂風驟起，只見一條大青蛇，從梁上飛將下來，蟠於椅上。帝驚倒，左右急救入宮，百官俱奔避。須臾，蛇不見了。忽然大雷大雨，加以冰雹，落到半夜方止，壞卻房屋無數。建寧四年二月，洛陽地震；又海水泛濫，沿海居民，盡被大浪捲入海中。光和元年，雌雞化雄。六月朔，黑氣十餘丈，飛入溫德殿中。秋七月，有虹現於玉堂，五原山岸，盡皆崩裂。種種不祥，非止一端。帝下詔問群臣以災異之由，議郎蔡邕上疏，以為霓墮雞化，乃婦寺干政之所致，言頗切直。帝覽奏嘆息，因起更衣。曹節在後竊視，悉宣告左右，遂以他事陷邕於罪，放歸田里。後張讓、趙忠、封諝、段圭、曹節、侯覽、蹇碩、程曠、夏惲、郭勝十人朋比為奸，號為「十常侍」。帝尊信張讓，呼為「阿父」。朝政日非，以致天下人心思亂，盜賊蜂起。

時鉅鹿郡有兄弟三人：一名張角，一名張寶，一名張梁。那張角本是個不第秀才，因入山採藥，遇一老人，碧眼童顏，手執藜杖，喚角至一洞中，以天書三卷授之，曰：「此名太平要術。汝得之，當代天宣化，普救世人。若萌異心，必獲惡報。」角拜問姓名。老人曰：「吾乃南華老仙也。」言訖，化陣清風而去。角得此書，曉夜功習，能呼風喚雨，號為「太平道人」。中平元年正月內，疫氣流行，張角散施符水，為人治病，自稱「大賢良師」。角有徒弟五百餘人，雲游四方，皆能書符念咒。次後徒眾日多，角乃立三十六方，大方萬餘人，小方六七千，各立渠帥，稱為將軍；訛言：「蒼天已死，黃天當立；歲在甲子，天下大吉。」令人各以白土，書「甲子」二字於家中大門上。青、幽、徐、冀、荊、揚、兗、豫八州之人，家家侍奉大賢良師張角名字。角遣其黨馬元義，暗齎金帛，結交中涓封胥，以為內應。角與二弟商議曰：「至難得者，民心也。今民心已順，若不乘勢取天下，誠為可惜。」遂一面私造黃旗，約期舉事；一面使弟子唐周，持書報封諝。唐周乃徑赴省中告變。帝召大將軍何進調兵擒馬元義，斬之；次收封諝等一干人下獄。張角聞知事露，星夜舉兵，自稱「天公將軍」，張寶稱「地公將軍」，張梁稱「人公將軍」；申言於眾曰：「今漢運將終，大聖人出。汝等皆宜順天從正，以樂太平。」四方百姓，裹黃巾從張角反者四五十萬。賊勢浩大，官軍望風而靡。何進奏帝火速降詔，令各處備禦，討賊立功；一面遣中郎將盧植、皇甫嵩、朱雋，各引精兵，分三路討之。

且說張角一軍，前犯幽州界分。幽州太守劉焉，乃江夏竟陵人氏，漢魯恭王之後也；當時聞得賊兵將至，召校尉鄒靖計議。靖曰：「賊兵眾，我兵寡，明公宜作速招軍應敵。」劉焉然其說，隨即出榜招募義兵。榜文行到涿縣，引出涿縣中一個英雄。那人不甚好讀書；性寬和，寡言語，喜怒不言於色；素有大志，專好結交天下豪傑；生得身長七尺五寸，兩耳垂肩，雙手過膝，目能自顧其耳，面如冠玉，唇如塗脂；中山靖王劉勝之後，漢景帝閣下玄孫：姓劉，名備，字玄德。昔劉勝之子劉貞，漢武時封涿鹿亭侯，後坐酌金失侯，因此遺這一支在涿縣。玄德祖劉雄，父劉弘。弘曾舉孝廉，亦嘗作吏，早喪。玄德孤幼，事母至孝；家貧，販屨織席為業。家住本縣樓桑村。其家之東南，有一大桑樹，高五丈餘，遙望之，童童如車蓋。相者云：「此家必出貴人。」玄德幼時，與鄉中小兒戲於樹下，曰：「我為天子，當乘此車蓋。」叔父劉元起奇其言，曰：「此兒非常人也！」因見玄德家貧，常資給之。年十五歲，母使游學，嘗師事鄭玄、盧植，與公孫瓚等為友。及劉焉發榜招軍時，玄德年已二十八歲矣。

當日見了榜文，慨然長嘆。隨後一人厲聲言曰：「大丈夫不與國家出力，何故長嘆？」玄德回視其人：身長八尺，豹頭環眼，燕頷虎鬚，聲若巨雷，勢如奔馬。玄德見他形貌異常，問其姓名。其人曰：「某姓張，名飛，字翼德。世居涿郡，頗有莊田，賣酒屠豬，專好結交天下豪傑。適纔見公看榜而嘆，故此相問。」玄德曰：「我本漢室宗親，姓劉，名備。今聞黃巾倡亂，有志欲破賊安民；恨力不能，故長嘆耳。」飛曰：「吾頗有資財，當招募鄉勇，與公同舉大事，如何？」玄德甚喜，遂與同入村店中飲酒。正飲間，見一大漢，推著一輛車子，到店門首歇了；入店坐下，便喚酒保：「快斟酒來吃，我待趕入城去投軍。」玄德看其人：身長九尺，髯長二尺；面如重棗，唇如塗脂；丹鳳眼，臥蠶眉：相貌堂堂，威風凜凜。玄德就邀他同坐，叩其姓名。其人曰：「吾姓關，名羽，字長生，後改雲長，河東解良人也。因本處勢豪，倚勢凌人，被吾殺了；逃難江湖，五六年矣。今聞此處招軍破賊，特來應募。」玄德遂以己志告之。雲長大喜。同到張飛莊上，共議大事。

飛曰：「吾莊後有一桃園，花開正盛；明日當於園中祭告天地，我三人結為兄弟，協力同心，然後可圖大事。」玄德、雲長齊聲應曰：「如此甚好。」次日，於桃園中，備下烏牛白馬祭禮等項，三人焚香再拜而說誓曰：「念劉備、關羽、張飛，雖然異姓，既結為兄弟，則同心協力，救困扶危；上報國家，下安黎庶；不求同年同月同日生，只願同年同月同日死。皇天后土，實鑒此心。背義忘恩，天人共戮！」誓畢，拜玄德為兄，關羽次之，張飛為弟。祭罷天地，復宰牛設酒，聚鄉中勇士，得三百餘人，就桃園中痛飲一醉。來日收拾軍器，但恨無馬匹可乘。正思慮間，人報有兩個客人，引一夥伴儅，趕一群馬，投莊上來。玄德曰：「此天佑我也！」三人出莊迎接。原來二客乃中山大商：一名張世平，一名蘇雙，每年往北販馬，近因寇發而回。玄德請二人到莊，置酒管待，訴說欲討賊安民之意。二客大喜，願將良馬五十匹相送；又贈金銀五百兩，鑌鐵一千斤，以資器用。玄德謝別二客，便命良匠打造雙股劍。雲長造青龍偃月刀，又名「冷艷鋸」，重八十二斤。張飛造丈八點鋼矛。各置全身鎧甲。共聚鄉勇五百餘人，來見鄒靖。鄒靖引見太守劉焉。三人參見畢，各通姓名。玄德說起宗派，劉焉大喜，遂認玄德為侄。

不數日，人報黃巾賊將程遠志統兵五萬來犯涿郡。劉焉令鄒靖引玄德等三人，統兵五百，前去破敵。玄德等欣然領軍前進，直至大興山下，與賊相見。賊眾皆披髮，以黃巾抹額。當下兩軍相對，玄德出馬，左有雲長，右有翼德，揚鞭大罵：「反國逆賊，何不早降！」程遠志大怒，遣副將鄧茂出戰。張飛挺丈八蛇矛直出，手起處，刺中鄧茂心窩，翻身落馬。程遠志見折了鄧茂，拍馬舞刀，直取張飛。雲長舞動大刀，縱馬飛迎。程遠志見了，早吃一驚，措手不及，被雲長刀起處，揮為兩段。後人有詩讚二人曰：

:::paragraphs{style="verse"}
英雄露穎在今朝，一試矛兮一試刀。

初出便將威力展，三分好把姓名標。
:::

眾賊見程遠志被斬，皆倒戈而走。玄德揮軍追趕，投降者不計其數，大勝而回。劉焉親自迎接，賞勞軍士。次日，接得青州太守龔景牒文，言黃巾賊圍城將陷，乞賜救援。劉焉與玄德商議。玄德曰：「備願往救之。」劉焉令鄒靖將兵五千，同玄德、關、張，投青州來。賊眾見救兵至，分兵混戰。玄德兵寡不勝，退三十里下寨。玄德謂關、張曰：「賊眾我寡；必出奇兵，方可取勝。」乃分關公引一千軍伏山左，張飛引一千軍伏山右，鳴金為號，齊出接應。次日，玄德與鄒靖引軍鼓噪而進。賊眾迎戰，玄德引軍便退。賊眾乘勢追趕，方過山嶺，玄德軍中一齊鳴金，左右兩軍齊出，玄德麾軍回身復殺。三路夾攻，賊眾大潰。直趕至青州城下，太守龔景亦率民兵出城助戰。賊勢大敗，剿戮極多，遂解青州之圍。後人有詩讚玄德曰：

:::paragraphs{style="verse"}
運籌決算有神功，二虎還須遜一龍。

初出便能垂偉績，自應分鼎在孤窮。
:::

龔景犒軍畢，鄒靖欲回。玄德曰：「近聞中郎將盧植與賊首張角戰於廣宗，備昔曾師事盧植，欲往助之。」於是鄒靖引軍自回，玄德與關、張引本部五百人投廣宗來。至盧植軍中，入帳施禮，具道來意。盧植大喜，留在帳前聽調。

時張角賊眾十五萬，植兵五萬，相拒於廣宗，未見勝負。植謂玄德曰：「我今圍賊在此，賊弟張梁、張寶在潁川，與皇甫嵩、朱雋對壘。汝可引本部人馬，我更助汝一千官軍，前去潁川打探消息，約期剿捕。」玄德領命，引軍星夜投潁川來。時皇甫嵩、朱儁領軍拒賊，賊戰不利，退入長社，依草結營。嵩與儁計曰：「賊依草結營，當用火攻之。」遂令軍士，每人束草一把，暗地埋伏。其夜大風忽起。二更以後，一齊縱火，嵩與儁各引兵攻擊賊寨，火焰張天，賊眾驚慌，馬不及鞍，人不及甲，四散奔走。

殺到天明，張梁、張寶引敗殘軍士，奪路而走。忽見一彪軍馬，盡打紅旗，當頭來到，截住去路。為首閃出一將：身長七尺，細眼長髯；官拜騎都尉；沛國譙郡人也，姓曹，名操，字孟德。操父曹嵩，本姓夏侯氏；因為中常侍曹騰之養子，故冒姓曹。曹嵩生操，小字阿瞞，一名吉利。操幼時，好游獵，喜歌舞；有權謀，多機變。操有叔父，見操游蕩無度，嘗怒之，言於曹嵩。嵩責操。操忽心生一計：見叔父來，詐倒於地，作中風之狀。叔父驚告嵩，嵩急視之，操故無恙。嵩曰：「叔言汝中風，今已愈乎？」操曰：「兒自來無此病；因失愛於叔父，故見罔耳。」嵩信其言。後叔父但言操過，嵩並不聽。因此，操得恣意放蕩。時人有橋玄者，謂操曰：「天下將亂，非命世之才不能濟。能安之者，其在君乎？」南陽何顒見操，言：「漢室將亡，安天下者，必此人也。」汝南許劭，有知人之名。操往見之，問曰：「我何如人？」劭不答。又問，劭曰：「子治世之能臣，亂世之奸雄也。」操聞言大喜。年二十，舉孝廉，為郎，除洛陽北都尉。初到任，即設五色棒十餘條於縣之四門，有犯禁者，不避富豪，皆責之。中常侍蹇碩之叔，提刀夜行，操巡夜拿住，就棒責之。由是，內外莫敢犯者，威名頗震。後為頓丘令。因黃巾起，拜為騎都尉，引馬步軍五千，前來潁川助戰。正值張梁、張寶敗走，曹操攔住，大殺一陣，斬首萬餘級，奪得旗旌、金鼓、馬匹極多。張梁、張寶死戰得脫。操見過皇甫嵩、朱儁，隨即引兵追襲張梁、張寶去了。

卻說玄德引關、張來潁川，聽得喊殺之聲，又望見火光燭天，急引兵來時，賊已敗散。玄德見皇甫嵩、朱儁，具道盧植之意。嵩曰：「張梁、張寶勢窮力乏，必投廣宗去依張角。玄德可即星夜往助。」玄德領命，遂引兵復回。到得半路，只見一簇軍馬，護送一輛檻車；車中之囚，乃盧植也。玄德大驚，滾鞍下馬，問其緣故。植曰：「我圍張角，將次可破；因角用妖術，未能即勝。朝廷差黃門左豐前來體探，問我索取賄賂。我答曰：『軍糧尚缺，安有餘錢奉承天使？』左豐挾恨，回奏朝廷，說我高壘不戰，惰慢軍心；因此朝廷震怒，遣中郎將董卓來代將我兵，取我回京問罪。」張飛聽罷，大怒，要斬護送軍人，以救盧植。玄德急止之曰：「朝廷自有公論，汝豈可造次？」軍士簇擁盧植去了。

關公曰：「盧中郎已被逮，別人領兵，我等去無所依，不如且回涿郡。」玄德從其言，遂引軍北行。行無二日，忽聞山後喊聲大震。玄德引關、張縱馬上高岡望之，見漢軍大敗，後面漫山塞野，黃巾蓋地而來，旗上大書「天公將軍」。玄德曰：「此張角也！可速戰。」三人飛馬引軍而出。張角正殺敗董卓，乘勢趕來，忽遇三人衝殺，角軍大亂，敗走五十餘里。三人救了董卓回寨。卓問三人現居何職。玄德曰：「白身。」卓甚輕之，不為禮。玄德出，張飛大怒曰：「我等親赴血戰，救了這廝，他卻如此無禮！若不殺他，難消我氣！」便要提刀入帳來殺董卓。正是：

:::paragraphs{style="verse"}
人情勢利古猶今，誰識英雄是白身？

安得快人如翼德，盡誅世上負心人！
:::

畢竟董卓性命如何，且聽下文分解。
`; // content.<lang>.md: the same Chinese text in both

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
const FONTS = {
  'Noto Serif TC': ['400', '700'], // 宋: the text; 700 for 第一回 and the title
  'LXGW WenKai TC': ['400'], // 楷: the couplet, the 詞 and the poems, the plate's note
  'Noto Sans TC': ['400'], // 黑: the fore-edge heads and folios, the plate's title
  'Source Serif 4': ['400', '400i'], // the imprint, with the book's title in italic
};

// ─── 4 · Build & show ───────────────────────────────────────────────────────
// #region voices: each face loads the slices of the characters it sets
// Fontsource cuts a Chinese face into about a hundred files; loadCjkFonts fetches those
// that hold the characters it is given (gotcha: cjk-fonts-slices). vertical: true loads the
// face again with its vertical punctuation forms, for the canvas.
const heads = markdown.match(/^# .*$/gm).join('').replace(/\{[^}]*\}/g, ''); // no attributes
const attr = (key) => markdown.match(new RegExp(`${key}="([^"]*)"`))?.[1] ?? '';
const verse = markdown.match(/:::paragraphs\{style="verse"\}[\s\S]*?\n:::/g).join('');
await loadFonts(FONTS, markdown); // the Latin files: the imprint
await loadCjkFonts({ [SONG]: ['400'] }, markdown, { vertical: true });
await loadCjkFonts({ [SONG]: ['700'] }, '三國演義第一回'); // no punctuation: no vertical twin
await loadCjkFonts({ [KAI]: ['400'] }, `${heads}${verse}${attr('editor')}${attr('note')}羅貫中著`,
  { vertical: true });
await loadCjkFonts({ [HEI]: ['400'] }, `${heads}第回一二三四五六七八九十`, { vertical: true });
// #endregion
await loadImage('peach-garden.jpg', asset('peach-garden-oath-1592-v2.jpg'));
const doc = await buildWithFonts(
  () => buildDocument({ markdown, resources }, config()), markdown);
showBook(doc, { title: t({ en: 'A vertical Chinese novel, bound on the right',
  es: 'Una novela china vertical, encuadernada por la derecha' }) });
offerPdf(() => renderToPdf(doc, { fontProvider: cjkPdfProvider, resourceBytes: imageBytes }),
  `${RECIPE}.pdf`);

Kit · core, fonts, viewer, pdf, images, cjk: the same in every recipe · 457 lines
// ─── 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 · images v1 ── recipes with pictures · postext.dev/cookbook ──────────
/** Registers a photo or PNG for the canvas and keeps its bytes for the PDF.
 *  fetch → ImageBitmap never taints the canvas (a plain cross-origin <img> would). */
async function loadImage(fileId, url) {
  const res = await fetch(url);
  if (!res.ok) throw new Error(`Image not found (${res.status}): ${url}`);
  const bytes = new Uint8Array(await res.arrayBuffer());
  registerResourceImage(fileId, await createImageBitmap(new Blob([bytes])));
  (loadImage.bytes ??= new Map()).set(fileId, bytes);
}

/** Registers SVG markup (drawn in code, or fetched) as a vector image. */
async function loadSvg(fileId, svg) {
  const img = new Image();
  img.src = `data:image/svg+xml;charset=utf-8,${encodeURIComponent(svg)}`;
  await img.decode();
  registerResourceImage(fileId, img);
  (loadImage.bytes ??= new Map()).set(fileId, new TextEncoder().encode(svg));
}

/** renderToPdf({ resourceBytes: imageBytes }) */
function imageBytes(fileId) { return loadImage.bytes?.get(fileId); }

/** renderToHtml({ resourceImageUrl: imageUrl }) */
function imageUrl(fileId) {
  const bytes = imageBytes(fileId);
  if (!bytes) return undefined;
  imageUrl.urls ??= new Map();
  if (!imageUrl.urls.has(fileId)) {
    const type = /\.svg$/i.test(fileId) ? 'image/svg+xml' : /\.png$/i.test(fileId) ? 'image/png' : 'image/jpeg';
    imageUrl.urls.set(fileId, URL.createObjectURL(new Blob([bytes], { type })));
  }
  return imageUrl.urls.get(fileId);
}

// ─── Kit · cjk 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 ───────────────────────────────────────────────────────────────────────