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Glossary

What is EPUB 3?

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EPUB 3 is the current version of the EPUB e-book standard, built on XHTML5, CSS, SVG and an HTML navigation document. Its latest revision, EPUB 3.3, became a W3C Recommendation in 2023.

Why it matters when you convert a PDF to EPUB

EPUB 3 is the format to produce today: it supports semantic markup for footnotes (epub:type), right-to-left and vertical writing, MathML, accessibility metadata and page lists that map back to the printed pages of the PDF. EPUBLab writes EPUB 3 and validates its benchmark output with EPUBCheck.

An EPUB 3 file can also carry an NCX table of contents so that very old EPUB 2 reading systems can still navigate it. Validators check EPUB 3 files against the EPUB 3.3 rules.

Related terms

EPUBCheck messages about this

  • PKG-001 Validating the EPUB against version … but detected version ….
  • OPF-001 There was an error when parsing the EPUB version: ….
  • HTM-004 Irregular DOCTYPE: found "…", expected "…".

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FAQ

What is EPUB 3?

EPUB 3 is the current version of the EPUB e-book standard, built on XHTML5, CSS, SVG and an HTML navigation document. Its latest revision, EPUB 3.3, became a W3C Recommendation in 2023.