Spazi uniformi in colonne giustificate strette

// ═══ Postext Cookbook · Nº 014 · Justification lab ════════════════════════════════
// https://postext.dev/en/cookbook/justification-lab
// Code: MIT · Text: original (CC BY 4.0) · Diagram: generated in code (CC BY 4.0)
// Fonts: Petrona, Bricolage Grotesque, Source Code Pro (SIL OFL 1.1) · Needs postext ≥ 1.25.0
// A type journal's essay set twice from one design, Knuth–Plass and greedy: the two page 2s
// side by side with their loose lines marked from the layout tree, then the published pages.
import {
  buildDocumentWithFonts, renderPageToCanvas, registerResourceImage, parseMarkdownWithIssues,
  findLooseLines,
} from 'https://esm.sh/postext';

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

// ─── 1 · Design ─────────────────────────────────────────────────────────────
// Graphite, paper and one highlighter yellow; col() links each colour to its palette entry.
const palette = {
  ink: '#1f2124', // text: a graphite near-black
  graphite: '#2e3136', // the accent: the opener band, the bench box, folios
  marker: '#ffe14d', // highlighter yellow: glue and loose lines, never type on white
  haze: '#c3c7cc', // type on graphite: the standfirst, the diagram's labels
  muted: '#66686c', // running heads, settings 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: 'defaults', value: { hex: palette.graphite, model: 'hex' } }, // no blue
];
const [TEXT, DISPLAY, MONO] = ['Petrona', 'Bricolage Grotesque', 'Source Code Pro'];
const [BODY, LEAD] = [9.5, 13]; // pt: body size and leading, the grid both columns share
// mm: an A5 trim, mirrored margins and a narrow gutter: two columns of about 40 characters
const [TRIM_W, TRIM_H, TOP, BOTTOM, INNER, OUTER, GUTTER] = [148, 210, 20, 20, 16, 13, 5];
const MEASURE = TRIM_W - INNER - OUTER; // mm: 119, the text width the opener aligns to
const caps = (size, weight = 500) => ({ fontFamily: MONO, fontSize: pt(size), fontWeight: weight,
  letterSpacing: pt(size * 0.16), textTransform: 'uppercase' }); // tracked mono labels

// #region answer: one design, two line breakers: Knuth–Plass inside fences, greedy without
// Knuth–Plass breaking, hyphenation and the widow, orphan and runt penalties are all on by
// default. A narrow column also needs a tighter fence round the glue, in multiples of a
// normal word space (defaults 0.6 and 2): lines past the upper fence cost more than any
// hyphen, so the breaker hyphenates or re-breaks the paragraph before it stretches that far.
const FENCES = { minWordSpacing: 0.8, maxWordSpacing: 1.6 };
const bodyText = { // config().bodyText
  fontFamily: TEXT, fontSize: pt(BODY), lineHeight: pt(LEAD), color: col('ink'),
  boldColor: col('ink'), italicColor: col('ink'), referenceColor: col('ink'),
  firstLineIndent: mm(4), indentAfterHeading: false, // justified and hyphenated by default
  ...FENCES,
};
// Hyphenation follows the document's locale:
const locale = t({ en: 'en-us', es: 'es' }); // config().locale: each edition's patterns
// The control: first-fit breaking, which sets each line once and moves on, with the widow and
// orphan guards off (runts are priced inside Knuth–Plass only). Same text, fonts and measure.
const GREEDY = { optimalLineBreaking: false, avoidWidows: false, avoidOrphans: false };
const control = () => ({ ...config(), bodyText: { ...bodyText, ...GREEDY } });
// #endregion

// #region opener: the title on a graphite band, with the diagram drawn in as an image element
const BAND = 104; // mm from the trim's top edge to the band's foot
const DIAGRAM = { y: 64, w: MEASURE + 8, h: 34 }; // mm: its top on the page, width, height
const LABEL = 7; // pt: the diagram's labels, tracked less than caps() so the legend fits
const text = (id, content, family, size, color, x, y, extra) => ({ kind: 'text', id, content,
  fontFamily: family, fontSize: pt(size), color: col(color), align: 'left', overflow: 'wrap',
  placement: { anchor: { to: 'page', edge: 'top-left' }, offset: { x: mm(x), y: mm(y) },
    size: { width: mm(MEASURE) } }, ...extra });
const opener = () => ({ // a function: the diagram's constants are defined further down
  enabled: true,
  slot: { elements: [
    // The band reaches below the diagram, so it sets the height the opener reserves; the H1's
    // default marginBottom adds a line of white, and the body starts on the second grid line
    // under the band.
    { kind: 'box', id: 'band', style: { backgroundColor: col('graphite') },
      placement: { anchor: { to: 'bleed', edge: 'top-left' },
        size: { width: 'fill', height: mm(BAND) } } },
    text('kicker', '{attr.kicker}', MONO, 7.5, 'marker', INNER, TOP, caps(7.5, 600)),
    text('title', '{titleText}', DISPLAY, 29, 'paper', INNER, TOP + 5, // one line in both
      { fontWeight: 800, lineHeight: 1.02 }),
    text('standfirst', '{attr.standfirst}', TEXT, 10.5, 'haze', INNER, TOP + 19,
      { italic: true, lineHeight: 1.3 }),
    { kind: 'image', id: 'diagram', resourceId: 'diagram', placement: { anchor: { to: 'page',
      edge: 'top-left' }, offset: { x: mm(INNER), y: mm(DIAGRAM.y) },
    size: { width: mm(DIAGRAM.w), height: mm(DIAGRAM.h) } } },
    // The diagram's labels are design text: set and tracked like the opener's other labels.
    ...diagramLabels().map(([id, words, x, y]) => text(id, words, MONO, LABEL, 'haze',
      INNER + x, DIAGRAM.y + y, { ...caps(LABEL), letterSpacing: pt(0.5) })),
  ] },
});
// #endregion

const HEAD_Y = 11; // mm from the top (bottom) edge: running heads in the margin, folios outside
const head = (id, content, parity, edge, x, extra) => ({ ...text(id, content, MONO, 7.5,
  'muted', 0, 0, caps(7.5)), parity, pages: 'body', align: edge.split('-')[1], // left | right
  placement: { anchor: { to: 'page', edge },
    offset: { x: mm(x), y: mm(edge.startsWith('top') ? HEAD_Y : -HEAD_Y) } }, ...extra });
const folio = { fontFamily: DISPLAY, fontWeight: 800, fontSize: pt(8), letterSpacing: pt(0),
  color: col('graphite') };
const header = { elements: [
  head('v-folio', '{pageNumber}', 'even', 'top-left', OUTER, folio),
  head('v-title', '{title} · {subtitle}', 'even', 'top-left', OUTER + 8),
  head('r-title', '{chapterTitle}', 'odd', 'top-right', -(OUTER + 8)),
  head('r-folio', '{pageNumber}', 'odd', 'top-right', -OUTER, folio),
] };
const footer = { elements: [head('drop-folio', '{pageNumber}', 'all', 'bottom-right', -OUTER,
  { ...folio, pages: 'opener' })] }; // the opener's folio drops to its foot

// #region bench: three slips in a 2 × 2 grid, each a nested box with a body style of its own
// A box sets all its :::columns in one body style, so each setting is a nested box; breaks="3"
// counts a nested box as one block. The bench floats to a page foot.
const [SLIP_GAP, FRAME] = [3, 4]; // mm: between slips; the bench's frame round them
const slip = (id, body) => ({ id, background: col('paper'), marginBottom: mm(SLIP_GAP),
  padding: { top: mm(2.2), right: mm(2.6), bottom: mm(2.4), left: mm(2.6) },
  titleStyle: { fontFamily: MONO, fontSize: pt(6.6), fontWeight: 600, color: col('muted'),
    gap: mm(1.6) }, // code keeps its case: textAlign, not TEXTALIGN
  body: { fontSize: pt(8.6), lineHeight: pt(11.6), firstLineIndent: pt(0), ...body } });
const calloutStyles = [
  { id: 'bench', span: 'page', placement: 'bottom', background: col('graphite'),
    columnGap: mm(FRAME), // the foot needs a FRAME too: the last slip's marginBottom is dropped
    padding: { top: mm(3.4), right: mm(FRAME), bottom: mm(FRAME), left: mm(FRAME) },
    titleStyle: { ...caps(7.5, 600), color: col('marker'), gap: mm(2.4) },
    body: { fontSize: pt(8.6), lineHeight: pt(11.6), color: col('paper'), textAlign: 'left',
      firstLineIndent: pt(0) } },
  slip('ragged', { textAlign: 'left' }), // ragged text keeps its words whole by default
  slip('unhyphenated', { hyphenation: false }), // justified, like the body text
  slip('justified', {}), // justified and hyphenated: the body text's own settings
  { id: 'settings', backgroundEnabled: false, marginTop: pt(3), marginBottom: pt(3), // config
    stripe: { enabled: true, side: 'left', width: pt(2), color: col('graphite') },
    padding: { top: pt(1), right: pt(0), bottom: pt(1), left: mm(3) },
    body: { fontFamily: MONO, fontSize: pt(7), lineHeight: pt(9.5), color: col('graphite'),
      firstLineIndent: pt(0) } },
];
// #endregion

const config = () => ({
  locale, colorPalette,
  page: { width: mm(TRIM_W), height: mm(TRIM_H), dpi: 150, margins: { top: mm(TOP),
    bottom: mm(BOTTOM), left: mm(INNER), right: mm(OUTER), mirror: true } },
  layout: { layoutType: 'double', gutterWidth: mm(GUTTER) },
  bodyText,
  headings: { fontFamily: DISPLAY, fontWeight: 800, color: col('ink'),
    levels: [ // the essay opens on a recto
      { level: 1, span: 'page', breakBefore: { enabled: true, parity: 'odd' },
        advancedDesign: opener() },
      { level: 2, fontSize: pt(11.5), lineHeight: pt(LEAD), marginTop: pt(LEAD),
        marginBottom: pt(0) },
    ] },
  paragraphStyles: [
    { id: 'colophon', fontFamily: MONO, fontSize: pt(6.6), lineHeight: pt(9), color: col('muted'),
      textAlign: 'left', firstLineIndent: pt(0), marginTop: pt(LEAD) },
  ],
  calloutStyles,
  header, footer,
});

// ─── 2 · Content ────────────────────────────────────────────────────────────
const markdown = String.raw`---
Esempio Markdown · 86 righe · content.en.md
title: "Galley"
subtitle: "Notes from the type bench · No. 12"
author: "Galley"
---

# The river problem {kicker="Galley · No. 12 · Justification" standfirst="Justify a narrow column and its word spaces are the first thing to open up. How a line breaker that weighs the whole paragraph keeps the grey even, and the eight settings that govern it."}

Hold a newspaper page at arm’s length and half close your eyes. In a good column the text turns into an even grey. In a bad one, pale channels wander down through it, from a gap in one line to the gap below it. Printers call them rivers. They form when the spaces open up on several lines at once and happen to fall in line, and nothing opens spaces faster than a narrow measure.

A column of forty characters has five or six word spaces to a line. Carry one long word on to the next line and those few spaces must share its whole width between them: each may have to grow to twice its width, or more. In a column twice as wide, twice as many spaces take up the same width, and each grows only half as much as before.

## Boxes, glue and penalties

In 1981, Donald E. Knuth and Michael F. Plass described a paragraph the way TeX still sees it. Words are boxes, fixed in width. The spaces between them are glue, with a natural width and a limit to how far it may stretch or shrink. Penalties mark the places where a line may end, each with a price: ending on a hyphen costs something, ending between two words costs nothing. The drawing at the head of this article shows one line in those terms, as measured and as set, with its glue stretched until the line fills the measure and the word that ran past it broken at a hyphen.

The breaker then prices every line by how far its glue had to move, cubing the figure so one very loose line costs more than a string of slightly loose ones, and then adds the penalties. Of all the ways to break the paragraph, it keeps the one whose total is lowest, looking back as far as the first line to find it.

## Greedy and total fit

The older method, first fit, survives on the web. It fills each line with as many words as will fit before moving on, and a line once set stays set, so one more short word taken now can leave the next line with a gap that no later break can close. The whole-paragraph method sets one line a little looser when that spares the next one a gap. Across a whole column the trade leaves fewer loose lines than first fit, and so fewer gaps that can line up into rivers.

## Fences for the glue

Two numbers fence the glue in: a space may shrink to 80 per cent of its natural width and grow to 160 per cent. Much tighter, and the breaker runs out of ways to fill a line; any looser, and the eye sees the gaps. Past the upper fence, every extra stretch costs more than any hyphen or short last line, so the breaker looks for another way to fill the line first.

:::callout{type="settings"}
minWordSpacing: 0.8

maxWordSpacing: 1.6
:::

:::callout{type="bench" title="Bench test · one paragraph, three settings"}
:::columns{count=2 breaks="3"}
:::callout{type="ragged" title="ragged · textAlign: 'left'"}
Unhyphenated justification in a narrow measure hands every shortfall to the few word spaces on the line. With hyphenation the line breaker can end a line inside a word too, and the slack is shared out in amounts too small to notice.
:::

:::callout{type="unhyphenated" title="justified · hyphenation: false"}
Unhyphenated justification in a narrow measure hands every shortfall to the few word spaces on the line. With hyphenation the line breaker can end a line inside a word too, and the slack is shared out in amounts too small to notice.
:::

:::callout{type="justified" title="justified · hyphenation: true"}
Unhyphenated justification in a narrow measure hands every shortfall to the few word spaces on the line. With hyphenation the line breaker can end a line inside a word too, and the slack is shared out in amounts too small to notice.
:::

The same words set three ways, in a measure a little narrower than these columns. Ragged text breaks only between words unless it is told to hyphenate. Justified without hyphens, a few spaces take up all the slack. With hyphens, the spaces stay even at the cost of a few broken words.
:::
:::

## Hyphens

Hyphens hand the breaker more places to end a line, and in a narrow measure they are not optional. Postext hyphenates with the TeX patterns of the document’s language, which it takes from an exact code: *en-us* for this issue and *es* for its Spanish edition. A code it lacks, such as *eu-ES*, falls back to American English with a warning. The patterns serve justified text only; ragged lines break only between words, so a narrow ragged column gets a deep rag.

## Widows, orphans and runts

A paragraph that breaks across columns leaves a line behind or carries one over. A lone first line at the foot of a column and a lone last line at the head of the next are the pair the style manuals forbid, though printers have never agreed which of the two is the widow. Postext settles it by position: avoidWidows applies at the foot of the column, avoidOrphans at its head.

:::callout{type="settings"}
widowPenalty: 1000

orphanPenalty: 1000

slackWeight: 10
:::

Each rule is a price in the breaker’s sums, weighed against the white space that obeying it would leave: a lone line costs its penalty, and the empty lines a split would leave at the foot of a column cost ten times the square of their number. The breaker takes the cheaper way.

A runt is a last line too short to stand alone: one word, or the tail of one, under a full paragraph. Postext prices it inside the line breaker, so a set of breaks that brings a second word down wins whenever the fences allow. When no other set of breaks stays inside the fences, it sets the paragraph one line shorter, tightening the spaces first and then, if it has to, the letters, by no more than ten thousandths of an em.

:::callout{type="settings"}
runtMinCharacters: 20

runtPenalty: 1000

maxRuntTracking: 10
:::

## What the eye forgives

A long word can still leave one line of a narrow column a shade looser than its neighbours, and a paragraph that must end somewhere will now and then end on a short line. The breaker can move the extra space from one line to another but cannot remove it. Near a long word it adds a trace to each of five lines rather than leave the whole amount in a single gap, where it would show as a hole in the grey of the column.

A line that still gapes is left to the editor, who can usually close it by changing one word in the sentence.

:::paragraphs{style="colophon"}
Galley is set in Petrona, Bricolage Grotesque and Source Code Pro (SIL Open Font License). Text and diagram: original, CC BY 4.0.
:::
`; // content.<lang>.md, inlined by the Cookbook


// #region art: boxes, glue and penalties: one line as measured and as set, and its resource
const resources = [{ id: 'diagram', typeId: 'figure', kind: 'svg', createdAt: 0, updatedAt: 0,
  svg: { fileId: 'diagram.svg', width: DIAGRAM.w * 10, height: DIAGRAM.h * 10 }, // 10 px a mm
  altText: t({ en: 'A line of word boxes whose last word overruns the measure; then the same '
    + 'line hyphenated, its springs stretched until it fills the measure exactly.',
  es: 'Una línea de cajas cuya última palabra rebasa la medida; después, la misma línea '
    + 'partida, con los muelles estirados hasta llenar la medida justa.' }) }];
// Word boxes in mm; the long last word may break at a hyphenation penalty after its first part.
const WORDS = [[14], [8], [17], [6.5], [13.5], [10], [16.7, 16]];
const [ROW_H, GLUE, HYPHEN, ROWS] = [4.4, 3.6, 2, [7, 20.5]]; // mm; ROWS: the rows' tops
const SET = WORDS.reduce((sum, w) => sum + w[0], HYPHEN); // the set line: boxes to the hyphen
const STRETCH = (MEASURE - SET) / (WORDS.length - 1) / GLUE; // what fills the measure: ×1.45
const R = (v) => Math.round(v * 100) / 100;
function spring(x, y, w) { // a zigzag of eight turns: glue, stretched or at rest
  const pts = Array.from({ length: 9 }, (_, i) => `${R(x + (i * w) / 8)} ${R(y + (i % 2 ? -1 : 1)
    * 0.9)}`);
  return `<path d="M${R(x)} ${R(y)}L${pts.join('L')}L${R(x + w)} ${R(y)}" fill="none" `
    + `stroke="${palette.marker}" stroke-width="0.45" stroke-linejoin="round"/>`;
}
function row(y, glue, broken) { // one line of boxes; `broken`: set up to the penalty
  let [x, out] = [0, ''];
  const box = (w, h = ROW_H) => { out += `<rect x="${R(x)}" y="${R(y + (ROW_H - h) / 2)}" `
    + `width="${R(w)}" height="${h}" rx="0.5" fill="${palette.paper}"/>`; x += w; };
  WORDS.forEach((word, i) => {
    if (i) { out += spring(x, y + ROW_H / 2, glue); x += glue; }
    box(word[0]);
    if (word.length === 1) return;
    // The penalty: a flagged break inside the word, marked by a yellow wedge. Taken, it sets
    // a hyphen (a short bar); passed over, the rest of the word runs on past the measure.
    out += `<path d="M${R(x - 1.1)} ${y - 2.6}h2.2l-1.1 1.9z" fill="${palette.marker}"/>`;
    if (broken) box(HYPHEN, 1); else box(word[1]);
  });
  return out;
}
function diagram() {
  const measure = `<path d="M${MEASURE - 0.2} 3V${ROWS[1] + ROW_H + 2}" ` // stops over the legend
    + `stroke="${palette.haze}" stroke-width="0.4" stroke-dasharray="0.8 0.8"/>`;
  return `<svg xmlns="http://www.w3.org/2000/svg" width="${DIAGRAM.w * 10}" `
    + `height="${DIAGRAM.h * 10}" viewBox="0 0 ${DIAGRAM.w} ${DIAGRAM.h}">`
    + `${row(ROWS[0], GLUE, false)}${row(ROWS[1], GLUE * STRETCH, true)}${measure}</svg>`;
}
function diagramLabels() { // [id, text, x, y] in mm from the diagram's top-left corner
  const k = STRETCH.toFixed(2).replace('.', t({ en: '.', es: ',' }));
  return [
    ['l-natural', t({ en: 'As measured: the word overruns',
      es: 'Medida natural: la palabra no cabe' }), 0, ROWS[0] - 5.5],
    ['l-set', t({ en: `As set: hyphenated, each space ×${k}`,
      es: `Compuesta: partida, cada espacio ×${k}` }), 0, ROWS[1] - 5.5],
    ['l-legend', t({ en: 'Box: a word · glue: a space · penalty: a break · dashes: the measure',
      es: 'Caja: palabra · cola: espacio · penalización: corte · trazos: la medida' }),
    0, ROWS[1] + ROW_H + 3.5],
  ];
}
// #endregion

// #region marks: the highlighter: loose lines, lone lines and runts read from the layout tree
// findLooseLines gives the justified lines whose word spaces stretch past a threshold, here the
// upper fence. The rest is read from the VDT: a line past 3× is set ragged (line.ragged), and a
// paragraph cut by a column is two blocks.
function marks(doc, page) {
  const body = doc.pages.flatMap((p) => p.columns.flatMap((c) => c.blocks)).filter((b) =>
    b.type === 'paragraph' && b.containerId === undefined && b.textAlign === 'justify');
  const loose = findLooseLines(doc, { threshold: FENCES.maxWordSpacing, pageIndex: page.index });
  const out = loose.map(({ x, y, width: w, height: h }) => ({ x, y, w, h, kind: 'loose' }));
  for (const column of page.columns) {
    for (const b of column.blocks.filter((x) => body.includes(x))) {
      const parts = body.filter((o) => o.contentIndex === b.contentIndex);
      b.lines.forEach((line) => {
        const at = { x: b.bbox.x, y: line.bbox.y, w: b.bbox.width, h: line.bbox.height, column };
        if (line.ragged) out.push({ ...at, kind: 'loose' }); // past 3×: no ratio, set ragged
        if (b.lines.length === 1 && parts.length > 1) { // Postext's names (see the essay):
          out.push({ ...at, kind: b === parts[0] ? 'widow' : 'orphan' }); // foot : head
        } else if (line.isLastLine && !/\s/.test(line.text.trim())) {
          out.push({ ...at, kind: 'runt' }); // one word alone on a paragraph's last line
        }
      });
    }
  }
  return out;
}
const TAGS = t({ en: { widow: 'widow', orphan: 'orphan', runt: 'runt' },
  es: { widow: 'viuda', orphan: 'huérfana', runt: 'corta' } });
function paintMarks(canvas, list, scale) {
  const ctx = canvas.getContext('2d');
  ctx.setTransform(scale, 0, 0, scale, 0, 0); // page px from here on
  for (const m of list) { // loose lines: a wash; lone lines and runts: a tag in the margin
    const loose = m.kind === 'loose';
    ctx.globalCompositeOperation = loose ? 'multiply' : 'source-over'; // the ink shows through
    ctx.fillStyle = loose ? palette.marker : palette.graphite;
    if (loose) { ctx.fillRect(m.x - 2, m.y + 1, m.w + 4, m.h - 1); continue; }
    ctx.font = `600 ${m.h * 0.48}px "${MONO}"`;
    const w = ctx.measureText(TAGS[m.kind]).width + m.h * 0.5;
    const x = m.column.index === 0 ? m.x - w - m.h * 0.35 : m.x + m.w + m.h * 0.35;
    ctx.fillRect(x, m.y + m.h * 0.12, w, m.h * 0.8);
    ctx.fillStyle = palette.marker;
    ctx.fillText(TAGS[m.kind], x + m.h * 0.25, m.y + m.h * 0.7);
  }
  ctx.setTransform(1, 0, 0, 1, 0, 0);
}
// #endregion

// #region compare: the control beside the published page, each with its count of marks
function compare(pairs) {
  document.head.insertAdjacentHTML('beforeend', `<style>
    #compare { background: ${palette.graphite}; color: ${palette.haze}; padding: 36px 24px 44px;
      font: 500 12px/1.4 "${MONO}", monospace; } #compare > * { max-width: 860px; margin: 0 auto; }
    #compare h2 { font: 800 clamp(30px, 6vw, 72px)/0.95 "${DISPLAY}", sans-serif; color: #fff;
      margin: 6px auto 26px; letter-spacing: -0.01em; } #compare figure { margin: 0; }
    #compare .kicker { color: ${palette.marker}; letter-spacing: .16em; text-transform: uppercase; }
    #compare .pair { display: grid; grid-template-columns: 1fr 1fr; gap: 28px; }
    #compare canvas { width: 100%; display: block; }
    #compare figcaption { margin-bottom: 12px; text-transform: uppercase; letter-spacing: .12em; }
    #compare figcaption b { display: block; margin-bottom: 6px; color: #fff; letter-spacing: 0;
      font: 800 clamp(18px, 2.4vw, 26px)/1 "${DISPLAY}"; text-transform: none; }
    @media (max-width: 640px) { #compare .pair { grid-template-columns: 1fr; } }</style>`);
  const section = Object.assign(document.createElement('section'), { id: 'compare' });
  section.innerHTML = `<p class="kicker">${t({ en: 'Same text · same design · page 2',
    es: 'El mismo texto · el mismo diseño · página 2' })}</p><h2>${t({
    en: 'Two line breakers', es: 'Dos formas de cortar' })}</h2><div class="pair"></div>`;
  for (const [name, doc] of pairs) {
    const page = doc.pages[1];
    const list = marks(doc, page); // one walk per edition: the counts and the paint share it
    const n = (...kinds) => list.filter((m) => kinds.includes(m.kind)).length;
    const counts = `${t({ en: 'loose', es: 'flojas' })} ${n('loose')} · `
      + `${t({ en: 'lone', es: 'solas' })} ${n('widow', 'orphan')} · `
      + `${t({ en: 'runts', es: 'cortas' })} ${n('runt')}`;
    const figure = document.createElement('figure');
    figure.innerHTML = `<figcaption><b>${name}</b><span>${counts}</span></figcaption>`;
    const canvas = figure.appendChild(document.createElement('canvas'));
    canvas.setAttribute('role', 'img');
    canvas.setAttribute('aria-label', `${name}, ${t({ en: 'page', es: 'página' })} 2: ${counts}`);
    renderPageToCanvas(page, doc, canvas, { scale: 1000 / page.width });
    paintMarks(canvas, list, 1000 / page.width);
    section.querySelector('.pair').append(figure);
  }
  document.getElementById('pages').before(section); // #pages: the desk showPages() builds
}
// #endregion

// ─── 3 · Fonts ──────────────────────────────────────────────────────────────
// Every face the pages and the comparison paint, loaded before the build.
const FONTS = { Petrona: ['400', '400i', '700', '700i'], 'Bricolage Grotesque': ['800'],
  'Source Code Pro': ['400', '500', '600'] };

// ─── 4 · Build & show ───────────────────────────────────────────────────────
await loadSvg('diagram.svg', diagram());
const build = (cfg) => buildDocumentWithFonts({ markdown, resources }, cfg(), kitFonts(FONTS));
const greedy = await build(control); // first: the control, for the comparison only
const doc = await build(config); // last: the published pages
showPages(doc, { title: t({ en: 'Justification lab', es: 'Laboratorio de justificación' }) });
compare([[t({ en: 'Greedy, no guards', es: 'Voraz, sin protecciones' }), greedy],
  ['Knuth–Plass', doc]]);
// The build's own report: parse issues (a ::: left open) and layout warnings.
const { issues } = parseMarkdownWithIssues(markdown);
kitStatus(t({ en: `${doc.pages.length} pages · parse issues ${issues.length} · layout warnings `,
  es: `${doc.pages.length} páginas · problemas de análisis ${issues.length} · avisos ` })
  + (doc.warnings?.length ?? 0));

Kit · core, fonts, viewer, images: uguale in ogni ricetta · 270 righe
// ─── Kit ── helpers shared by every Cookbook recipe · postext.dev/cookbook ─────

// ─── Kit · core v1 ── the same in every recipe · postext.dev/cookbook
function mm(value) { return { value, unit: 'mm' }; }
function pt(value) { return { value, unit: 'pt' }; }
function em(value) { return { value, unit: 'em' }; }
/** The sample language's string: t({ en: 'Figure', es: 'Figura' }). */
function t(strings) { return strings[LANG] ?? Object.values(strings)[0]; }
/** A file in this recipe's assets folder, served from the Postext repo by jsDelivr. */
function asset(file) { return `https://cdn.jsdelivr.net/gh/drnachio/postext@main/cookbook/${RECIPE}/assets/${file}`; }

// ─── Kit · fonts v3 ── the same in every recipe · postext.dev/cookbook
// Postext loads the faces a config asks for before layout (prepareFonts,
// buildDocumentWithFonts) and asks the kit for the files: Fontsource's, the
// files the PDF embeds too.

/** The options of buildDocumentWithFonts / prepareFonts / withLoadedFonts:
 *  the Fontsource resolver, and the faces of FONTS loaded with the ones the
 *  config names. FONTS = { 'Family Name': ['400', '400i', '700'] }. */
function kitFonts(FONTS = {}) {
  const faces = Object.entries(FONTS).flatMap(([family, specs]) => specs.map((spec) =>
    ({ family, weight: parseInt(spec, 10), style: spec.endsWith('i') ? 'italic' : 'normal' })));
  return { resolve: fontsourceResolver, faces };
}

/** A face's Fontsource files, in a fixed order: latin, then latin-ext and greek
 *  when `text` needs them and the family ships them (kitSubsetsFor), each with
 *  its unicode-range. Null for a weight or slant Fontsource does not ship. */
async function fontsourceResolver(family, weight, style, { text = '' } = {}) {
  const id = fontsourceId(family);
  const meta = await fontsourceMeta(family);
  if (meta && !(meta.weights.includes(weight) && meta.styles.includes(style))) return null;
  kitStatus('Loading fonts…');
  const at = await fontsourceAt(id);
  return ['latin', ...kitSubsetsFor(text, meta)].map((subset) => ({
    source: `${at}files/${id}-${subset}-${weight}-${style}.woff2`,
    unicodeRange: kitRanges()[subset],
  }));
}

/** The unicode-range of each Fontsource file the kit loads (a function: the
 *  kit is inlined after the pen's code, which runs before a const would be set). */
function kitRanges() {
  return {
    latin: 'U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,'
      + 'U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD',
    'latin-ext': 'U+0100-02BA,U+02BD-02C5,U+02C7-02CC,U+02CE-02D7,U+02DD-02FF,U+0304,U+0308,U+0329,'
      + 'U+1D00-1DBF,U+1E00-1E9F,U+1EF2-1EFF,U+2020,U+20A0-20AB,U+20AD-20C0,U+2113,U+2C60-2C7F,U+A720-A7FF',
    greek: 'U+0370-03FF',
  };
}

/** For the cjk, arabic and comics blocks, which add their own files: the
 *  faces of `faces` = { 'Family Name': ['400', '400i', '700'] }. `text` is the sample:
 *  č ł † α χ also load latin-ext and greek files (kitSubsetsFor). With
 *  `optional`, a face Fontsource does not ship is skipped instead of failing.
 *  The files are added once all have loaded, in the order asked (latin, then
 *  latin-ext, then greek), whatever order they arrive in: the last one added
 *  wins a character two files hold. Resolves to the number of faces added. */
async function loadFonts(faces, text = '', { optional = false } = {}) {
  kitStatus('Loading fonts…');
  const ranges = kitRanges();
  const jobs = [];
  for (const [family, specs] of Object.entries(faces)) {
    const id = fontsourceId(family);
    const todo = [...new Set(specs)].map((spec) => [parseInt(spec, 10), spec.endsWith('i') ? 'italic' : 'normal'])
      .filter(([weight, style]) => !hasFace(family, weight, style)); // before any await
    const at = fontsourceAt(id);
    const meta = optional || /[^\0-ÿ]/u.test(text) ? await fontsourceMeta(family) : null;
    const subsets = ['latin', ...kitSubsetsFor(text, meta)];
    for (const [weight, style] of todo) {
      if (optional && !(meta?.weights.includes(weight) && meta.styles.includes(style))) continue;
      for (const subset of subsets) {
        const url = `${await at}files/${id}-${subset}-${weight}-${style}.woff2`;
        const face = new FontFace(family, `url(${url}) format('woff2')`,
          { weight: String(weight), style, unicodeRange: ranges[subset] });
        jobs.push(face.load().catch(() => {
          if (subset === 'latin' && !optional) throw new Error(`Fontsource has no ${family} ${weight} ${style}`);
        }));
      }
    }
  }
  const ready = await Promise.all(jobs).catch((error) => { kitFail(error); throw error; });
  return ready.filter((face) => face && document.fonts.add(face)).length;
}

/** A loaded FontFace covers this family, weight and style (fonts.check() would
 *  also say yes for families nobody declared). */
function hasFace(family, weight, style) {
  for (const face of document.fonts) {
    if (face.status !== 'loaded' || face.style !== style) continue;
    if (face.family.replace(/^["']|["']$/g, '') !== family) continue;
    const [low, high = low] = face.weight.split(' ').map(Number);
    if (weight >= low && weight <= high) return true;
  }
  return false;
}

/** The files beyond latin `text` needs that `meta`'s family ships. */
function kitSubsetsFor(text, meta) {
  return [[/[Ā-˿ᴀ-ᶿḀ-ỿ†ℓⱠ-Ɀ꜠-ꟿ]/u, 'latin-ext'], [/[Ͱ-Ͽ]/u, 'greek']]
    .filter(([re, x]) => re.test(text) && meta?.subsets?.includes(x)).map(([, x]) => x);
}

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

/** A package's folder at the one version @5 names now (#766). */
function fontsourceAt(id, u = `https://cdn.jsdelivr.net/npm/@fontsource/${id}@`) {
  return (fontsourceAt.c ??= {})[id] ??= fetch(u + '5/package.json').then((r) => r.json())
    .then((p) => p.version || 5, () => 5).then((v) => `${u}${v}/`);
}

/** The family's Fontsource metadata (weights, styles, subsets), or null. */
function fontsourceMeta(family) {
  fontsourceMeta.cache ??= new Map();
  const id = fontsourceId(family);
  if (!fontsourceMeta.cache.has(id)) {
    fontsourceMeta.cache.set(id, fetch(`https://api.fontsource.org/v1/fonts/${id}`)
      .then((res) => (res.ok ? res.json() : null), () => null));
  }
  return fontsourceMeta.cache.get(id);
}

// ─── Kit · viewer v2 ── the same in every recipe · postext.dev/cookbook
/** The pages as spreads on a dark desk, page 1 alone, then verso | recto,
 *  each painted when it scrolls near. Other options go to renderPageToCanvas. */
function showPages(docs, { title, width = 460, ...render } = {}) {
  const root = viewer(title);
  const pages = [docs].flat().flatMap((doc) =>
    doc.pages.map((page) => ({ doc, page, n: (doc.pageIndexOffset ?? 0) + page.index })));
  const spreads = [];
  let verso = null;
  for (const p of pages) {
    if (p.n % 2 === 1) { if (verso) spreads.push([verso, null]); verso = p; }
    else { spreads.push([verso, p]); verso = null; }
  }
  if (verso) spreads.push([verso, null]);
  const density = Math.min(window.devicePixelRatio || 1, 2);
  showPages.painter?.disconnect();
  const painter = new IntersectionObserver((entries) => {
    for (const { isIntersecting, target } of entries) {
      if (!isIntersecting) continue;
      painter.unobserve(target);
      const { doc, page } = target.postext;
      renderPageToCanvas(page, doc, target, { ...render, scale: (width * density) / page.width });
    }
  }, { rootMargin: '800px' });
  showPages.painter = painter;
  root.replaceChildren(...spreads.map((pair) => {
    const spread = document.createElement('div');
    spread.className = 'pt-spread';
    for (const p of pair) {
      const figure = document.createElement('figure');
      if (p) {
        const label = p.page.pageLabel || String(p.n + 1);
        const canvas = document.createElement('canvas');
        canvas.postext = p;
        canvas.style.aspectRatio = `${p.page.width} / ${p.page.height}`;
        canvas.setAttribute('role', 'img');
        canvas.setAttribute('aria-label', `Page ${label}`);
        const folio = document.createElement('figcaption');
        folio.textContent = label;
        figure.append(canvas, folio);
        painter.observe(canvas);
      } else figure.className = 'pt-blank';
      spread.append(figure);
    }
    return spread;
  }));
  kitStatus(`${pages.length} ${pages.length === 1 ? 'page' : 'pages'}`);
  document.documentElement.dataset.postext = 'ready';
  return pages.length;
}

/** The desk, the bar and the error reporting, created once. */
function viewer(title) {
  if (!document.getElementById('pt-kit')) {
    document.head.insertAdjacentHTML('beforeend', `<style id="pt-kit">
      :root { color-scheme: dark; }
      body { margin: 0; background: #0e1014; color: #b9bcc4; font: 13px/1.45 system-ui, sans-serif; }
      #pt-bar { position: sticky; top: 0; z-index: 1; display: flex; flex-wrap: wrap; align-items: center;
        gap: 6px 16px; padding: 10px 16px; background: rgb(14 16 20 / .92); backdrop-filter: blur(6px);
        border-bottom: 1px solid #23262d; }
      #pt-bar strong { color: #f4f1ea; font-weight: 600; }
      #pt-actions { display: flex; gap: 12px; margin-left: auto; }
      #pt-actions a, #pt-actions button { color: #d8a21a; font: inherit; background: none; border: 0; padding: 0; cursor: pointer; }
      #pages { display: grid; justify-items: center; gap: 48px; padding: 32px 16px 72px; }
      .pt-spread { display: flex; }
      .pt-spread figure { margin: 0; width: min(460px, 44vw); }
      .pt-spread canvas { display: block; width: 100%; background: #fff;
        box-shadow: 0 1px 2px rgb(0 0 0 / .5), 0 22px 44px -16px rgb(0 0 0 / .8); }
      .pt-spread figure:first-child canvas { box-shadow: inset -14px 0 14px -14px rgb(0 0 0 / .18), 0 1px 2px rgb(0 0 0 / .5), 0 22px 44px -16px rgb(0 0 0 / .8); }
      .pt-spread figcaption { margin-top: 10px; text-align: center; font: 600 10px/1 system-ui, sans-serif;
        letter-spacing: .18em; text-transform: uppercase; color: #6c7079; }
      .pt-blank { visibility: hidden; }
      @media (max-width: 760px) {
        .pt-spread { flex-direction: column; gap: 32px; }
        .pt-spread figure { width: min(460px, 92vw); }
        .pt-blank { display: none; }
      }
    </style>`);
    document.body.insertAdjacentHTML('afterbegin',
      '<header id="pt-bar"><strong id="pt-title"></strong><span id="pt-status" role="status"></span><span id="pt-actions"></span></header>');
    document.getElementById('pt-title').textContent = document.title || 'Postext';
    addEventListener('error', (event) => kitFail(event.error ?? event.message));
    addEventListener('unhandledrejection', (event) => kitFail(event.reason));
  }
  if (title) document.getElementById('pt-title').textContent = title;
  return document.getElementById('pages')
    ?? document.body.appendChild(Object.assign(document.createElement('main'), { id: 'pages' }));
}

function kitStatus(text) {
  viewer();
  document.getElementById('pt-status').textContent = text;
}

function kitFail(error) {
  document.documentElement.dataset.postext = 'error';
  kitStatus(`Error: ${error?.message ?? error}`);
}

// ─── Kit · images v3 ── recipes with pictures · postext.dev/cookbook
/** Registers a photo or PNG for the canvas and keeps its bytes for the PDF.
 *  fetch → ImageBitmap never taints the canvas (a plain cross-origin <img> would). */
async function loadImage(fileId, url) {
  const res = await fetch(url);
  if (!res.ok) throw new Error(`Image not found (${res.status}): ${url}`);
  const bytes = new Uint8Array(await res.arrayBuffer());
  registerResourceImage(fileId, await createImageBitmap(new Blob([bytes])));
  (loadImage.bytes ??= new Map()).set(fileId, bytes);
}

/** Registers SVG markup as a vector image, its fonts inside (inlineSvgFonts, ≥ 1.25).
 *  `options` go to registerResourceImage: { singleInk: true } tints it on the canvas. */
async function loadSvg(fileId, svg, options) {
  if (typeof inlineSvgFonts === 'function') svg = await inlineSvgFonts(svg, svgFaces);
  const img = new Image();
  img.src = `data:image/svg+xml;charset=utf-8,${encodeURIComponent(svg)}`;
  await img.decode();
  registerResourceImage(fileId, img, options);
  (loadImage.bytes ??= new Map()).set(fileId, new TextEncoder().encode(svg));
}

/** A face's Fontsource files: nearest weight; latin + what the SVG sets. */
async function svgFaces(family, weight, style, { codePoints = [] } = {}) {
  const [id, m] = [fontsourceId(family), await fontsourceMeta(family)];
  const w = m?.weights.reduce((a, b) => (Math.abs(b - weight) < Math.abs(a - weight) ? b : a)) ?? weight;
  const s = m?.styles.includes(style) === false ? 'normal' : style;
  return Promise.all(['latin', ...kitSubsetsFor(String.fromCodePoint(...codePoints), m)].map(async (x) => new Uint8Array(
    await (await fetch(`${await fontsourceAt(id)}files/${id}-${x}-${w}-${s}.woff2`)).arrayBuffer())));
}

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

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

// ─── /Kit ───────────────────────────────────────────────────────────────────────