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Guided Navigation

Guided Navigation (GND) is the JSON tree this library extracts from HTML/XHTML, before turning it into utterances (see Utterance Extraction).

Building a GND document

import { makeGnd } from "@readium/speech";

const gnd = makeGnd(`
  <section epub:type="chapter">
    <h1>Chapter One</h1>
    <p>It was a dark and stormy night.</p>
  </section>
`);
// gnd.guided: GndObject[]
function makeGnd(input: string, mediaType?: GndMediaType): GndDocument;

interface GndDocument {
  links?: unknown[];
  guided: GndObject[];
}

mediaType is "text/html" | "application/xhtml+xml". Omit it to sniff from input (XML declaration, xmlns:epub, XHTML doctype → XHTML; else HTML).

Skip the GndDocument wrapper by calling parseMarkup(html): GndObject[] directly.

Parsing uses the native DOMParser — no HTML/XML library bundled or loaded at runtime.

GndObject

type GndRole = string; // open-ended, see roles.ts

interface GndText {
  language: string;
  plain?: string;
  ssml?: string;
}

interface GndObject {
  role?: GndRole[];
  text?: string | GndText;
  description?: string;
  imgref?: string;
  audioref?: string;
  videoref?: string;
  textref?: string;
  id?: string;
  children?: GndObject[];
}
  • role can have multiple entries: tag name, ARIA role, epub:type all contribute, in that order (e.g. <section epub:type="chapter"> → ["section", "chapter"]). role="presentation"/"none" overrides everything to ["presentation"].
  • text is a plain string when unformatted, a GndText when it needs SSML (inline formatting, a language shift, or an embedded footnote/pagebreak/image mid-sentence). ssml marks embedded objects with a <readium:noteref id="..." />-style placeholder whose id matches a sibling in children.
  • imgref/audioref/videoref are a media element's src. textref is an href — reused for navigational-list items (toc, index...), noteref/backlink/biblioref/glossref, and plain links.
  • description is a node's accessible name (aria-label, alt, <figcaption>...) when it differs from its visible text.
  • Empty/presentational/aria-hidden/hidden content and role-less wrapper <div>s are dropped from the tree, not kept as empty nodes.
  • A block whose only child has no role/id of its own gets that child's text/refs hoisted into it: <p><a href="...">Cover</a></p> → { role: ["paragraph"], text: "Cover", textref: "..." }, not a nested anonymous child.

Footnotes and pagebreaks

Both are read out of narrative order, so the converter handles them specially:

  • noteref (<a role="doc-noteref" href="#note1">) resolves its href and embeds the target's whole subtree as children — no second lookup needed. Unresolvable hrefs get a plain textref child instead. The footnote is suppressed from also appearing at its original location.
  • pagebreak (<span epub:type="pagebreak" title="42">) carries its label as text. Mid-sentence, it's a <readium:pagebreak id="..." /> placeholder in that sentence's ssml, with the pagebreak node as a sibling children entry.

Roles

Three independent sources, mapped in src/gnd/roles.ts:

  1. Element type — <h1> → heading1, <nav> → navigation, <blockquote> → blockquote, etc.
  2. ARIA role — role="doc-chapter" → chapter, role="figure" → figure, etc. role="heading" reads its level from aria-level (default 2).
  3. epub:type — epub:type="chapter" → chapter, epub:type="pagebreak" → pagebreak, etc. (XHTML only, see below).

epub:type requires XHTML

epub:type only means anything in namespace-aware XHTML. Pass a complete XHTML document (xmlns:epub on the root):

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops">
<head><meta charset="utf-8"/><title>...</title></head>
<body>
  <section epub:type="chapter">...</section>
</body>
</html>

ARIA roles and native elements work as plain HTML fragments.

Fixtures

fixtures/ is a language-agnostic conformance suite for this stage plus utterance extraction — see fixtures/README.md and Testing.