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Glossary

What is an EPUB CFI?

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An EPUB CFI (Canonical Fragment Identifier) is a standard way to point at any location or range inside an EPUB, written as epubcfi(…) with a path through the package and the document. Reading systems can use it for bookmarks, highlights and reading positions.

Why it matters when you convert a PDF to EPUB

A reading position stored as a CFI depends on the structure of the EPUB: the spine order and the elements in each chapter. If you convert a PDF again and the structure changes, saved positions and highlights may no longer point to the same sentence.

The specification, EPUB Canonical Fragment Identifiers 1.1, was published by the IDPF in 2017; whether and how a given app uses CFIs internally is up to that app.

How EpubCC handles it: chapters and the identifier are derived from the content, so converting the same PDF with the same engine version gives the same structure, which keeps positions stable. A new engine version that improves paragraphs or chapters can change the structure.

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What is an EPUB CFI?

An EPUB CFI (Canonical Fragment Identifier) is a standard way to point at any location or range inside an EPUB, written as epubcfi(…) with a path through the package and the document. Reading systems can use it for bookmarks, highlights and reading positions.