# EPUBCheck OPF-090: It is encouraged to use MIME media type…

Source: https://epublab.com/epubcheck/opf-090/ (updated 2026-11-03)

EPUBCheck OPF-090 is a usage message: “It is encouraged to use MIME media type "…" instead of "…".” The manifest uses an older media type where a newer one is preferred; EPUBCheck names both.

- Official message (EPUBCheck 5.4.0): It is encouraged to use MIME media type "%1$s" instead of "%2$s".
- Default severity: Usage

## Typical causes

- Manifests written before the current media types were registered.

## How to fix it

- Change the media-type to the one EPUBCheck suggests. The file itself does not change.

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