# MED_011: chapter in two media overlays, how to fix it

Source: https://epubcc.com/epubcheck/med_011/ (updated 2026-11-04)

EPUBCheck MED_011 is an error message: “EPUB Content Document referenced from multiple Media Overlay Documents.” A content document is referenced from more than one media overlay. The media-overlay attribute names a single SMIL file per chapter, so the narration of one chapter has to be in one overlay.

- Official message (EPUBCheck 5.4.0): EPUB Content Document referenced from multiple Media Overlay Documents.
- Default severity: Error

## Typical causes

- Two SMIL files that both point to the same chapter, for example after splitting the narration.
- A chapter split or merged after the overlays were generated.

## How to fix it

1. Find which SMIL files reference the chapter EPUBCheck names (their text elements' src attributes).
2. Merge the narration of that chapter into one SMIL file, or split the chapter so each overlay narrates its own document.
3. Make the media-overlay attribute of the chapter's manifest item name the remaining overlay.
4. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

## When it's not this

If only the media-overlay attribute names the wrong overlay, the error is MED_012.

## Sources

- EPUB 3.3, §9.3.5.1 Including media overlays: https://www.w3.org/TR/epub-33/#sec-package-including (read 2026-11-04)

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