# EPUBCheck RSC-026: URL … leaks outside the container (it…

Source: https://epublab.com/epubcheck/rsc-026/ (updated 2026-11-03)

EPUBCheck RSC-026 is an error message: “URL "…" leaks outside the container (it is not a valid-relative-ocf-URL-with-fragment string).” A relative URL climbs above the root of the EPUB (too many ../), pointing outside the container.

- Official message (EPUBCheck 5.4.0): URL "%1$s" leaks outside the container (it is not a valid-relative-ocf-URL-with-fragment string)
- Default severity: Error

## Typical causes

- A path written for the original folder structure that has one ../ too many.

## How to fix it

- Count the folders between the document and the target and correct the relative path so it stays inside the book.

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