# EPUBCheck OPF-088: unknown epub:type value, how to fix it

Source: https://epubcc.com/epubcheck/opf-088/ (updated 2026-11-04)

EPUBCheck OPF-088 is a usage message: “Unrecognized epub:type value "…".” An epub:type value is not in the EPUB structural semantics vocabulary, so reading apps will ignore it. It is a usage note (shown with -u) and does not make the EPUB invalid.

- Official message (EPUBCheck 5.4.0): Unrecognized epub:type value "%1$s".
- Default severity: Usage

## Typical causes

- A misspelling such as "footnotes" on a single note.
- A value invented for styling, such as epub:type="red-box".
- A value from another vocabulary used without its prefix.

## How to fix it

1. Read the value EPUBCheck quotes.
2. Use the correct value from the vocabulary (footnote, endnote, chapter, toc…) if one fits.
3. For styling, use class instead; for another vocabulary, give the value a declared prefix.

## When it's not this

If the value exists but is deprecated, EPUBCheck reports OPF-086b.

## Sources

- EPUB 3.3, §C.2 The epub:type attribute: https://www.w3.org/TR/epub-33/#sec-epub-type-attribute (read 2026-11-04)

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EpubCC.