# OPF-086c: deprecated reserved prefix, how to fix it

Source: https://epubcc.com/epubcheck/opf-086c/ (updated 2026-11-04)

EPUBCheck OPF-086c is a warning message: “the "…" reserved prefix is deprecated.” A reserved prefix that EPUB has deprecated is used or declared, and EPUBCheck names it. In EPUBCheck 5.4.0 these are the xsd, msv and prism prefixes, which EPUB 3.3 no longer recommends.

- Official message (EPUBCheck 5.4.0): the "%1$s" reserved prefix is deprecated.
- Default severity: Warning

## Typical causes

- Metadata or properties that use the xsd prefix, often copied from old templates.
- Magazine content using the msv or prism prefixes in epub:type.
- A prefix attribute that still declares one of these prefixes.

## How to fix it

1. Find where the prefix EPUBCheck names is used.
2. Remove the property or value that depends on it if reading apps do not need it.
3. If you must keep it, declare the vocabulary under a prefix of your own in the prefix attribute instead of relying on the reserved one.

## When it's not this

If a reserved prefix is re-declared with a different URI, that is OPF-007.

## Sources

- EPUB 3.3, §D.1.5 Reserved prefixes: https://www.w3.org/TR/epub-33/#sec-reserved-prefixes (read 2026-11-04)

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