# EPUBCheck MED_017: overlay fragment not an id, how to fix it

Source: https://epubcc.com/epubcheck/med_017/ (updated 2026-11-04)

EPUBCheck MED_017 is a warning message: “URL fragment should indicate an element ID, but found '#…'.” A media overlay text reference uses a fragment that is not an element id. For XHTML chapters, EPUB recommends pointing to an element by its id; other fragment schemes may not be supported by reading apps. EPUBCheck warns and shows the fragment.

- Official message (EPUBCheck 5.4.0): URL fragment should indicate an element ID, but found '#%1$s'.
- Default severity: Warning

## Typical causes

- Text fragment or character-offset schemes written by an alignment tool.
- A fragment with a typo or a leading character that is not part of the id.

## How to fix it

1. Give the phrase an element with an id in the chapter, for example <span id="s12">.
2. Point the text src to it, as chapter1.xhtml#s12.
3. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

## When it's not this

If the target is an SVG document, the fragment should be an SVG fragment identifier (MED_018).

## Sources

- EPUB 3.3, §9.3.2.2 Referencing document fragments: https://www.w3.org/TR/epub-33/#sec-media-overlays-fragids (read 2026-11-04)

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