EPUB

For EPUB the extension builds the same index it builds for HTML, out of the same document nodes: an unnumbered level-one heading, a section carrying the qi-index id, letter groups, the nested entry list, numbered locator links and cross-references, with the same classes on the same pieces. Everything on the HTML page applies here, including how anchors are minted and how a heading mark’s anchor is moved. No stylesheet is added.

What differs is not the index but the container it is written into. Pandoc’s EPUB writer splits the document at its top-level headings and writes each piece as an XHTML file of its own inside the EPUB, so the index lands in a file of its own and a locator link crosses files — text/ch003.xhtml#qi-mark-7 rather than #qi-mark-7. That is the writer’s doing and needs nothing from you; the links resolve inside the book.

Two differences are worth knowing about before you render.

A book is one process. Quarto renders an EPUB book the way it renders a PDF one: all the chapters go through a single Pandoc process. So the extension sees the whole book at once, and each name your indexes: metadata declares gets a section of its own, headed with that declaration’s own title — as it does in an HTML book too, which reaches the same result by another route, aggregating a chapter per process through a per-chapter record. The Named indexes page describes the declaration; the Books page describes the aggregation.

Where one process does make a difference is the scope a page range pairs in: a range you open in one chapter and close in another pairs in an EPUB book and contributes a single locator, where the same two marks in an HTML book cannot see each other and index on their own.

Locators are sequence numbers, not pages. An EPUB has no pages: what a reader sees depends on their device and their type size, so there is no page number to print. An entry’s locators are the numbered links HTML uses — 1, 2, 3 for the first, second and third time the term is marked, restarting at 1 for each entry — and each one takes the reader to the passage rather than naming where it sits. If you want page numbers you want the LaTeX and PDF back-end.