# EPUBCheck HTM-010: Namespace … is unusual for the prefix…

Source: https://epublab.com/epubcheck/htm-010/ (updated 2026-11-03)

EPUBCheck HTM-010 is a usage message: “Namespace "…" is unusual for the prefix "epub".” The epub prefix is bound to an unexpected namespace, so epub:type and other epub attributes may be ignored.

- Official message (EPUBCheck 5.4.0): Namespace "%1$s" is unusual for the prefix "epub".
- Default severity: Usage

## Typical causes

- A typo in the namespace declaration.

## How to fix it

- Declare it as xmlns:epub="http://www.idpf.org/2007/ops" on the html element.

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