EpubCCEPUBCheck OPF-045: circular fallback chain
Updated:
EPUBCheck OPF-045 is an error message: “Encountered circular reference in fallback chain.” A manifest fallback chain is circular: following the fallback attributes leads back to an item already in the chain. A reading app looking for a format it can render would loop forever.
The official message
Encountered circular reference in fallback chain.
- Default severity
- Error. The EPUB breaks a rule of the specification and is invalid. Stores and Send to Kindle may reject it, and EPUBCheck exits with status 1.
- EPUBCheck version
- 5.4.0
Typical causes
- Two items that name each other as fallback.
- A longer chain whose last item points back to the first.
- Fallbacks edited by hand without checking the whole chain.
How to fix it
- Start at the item EPUBCheck points to and write down each fallback in turn.
- Remove the fallback attribute from the item that points back into the chain.
- Make sure the chain ends at a content document (for spine items) or a core media type.
When it's not this
If a fallback points to an id that does not exist, that is OPF-040.
Terms used here
Other OPF messages
OPF-044Spine item with non-standard media-type "…" has no EPUB content document fallback.OPF-043Spine item with non-standard media-type "…" has no fallback.OPF-042"…" is not a permissible spine media-type.OPF-048Package tag is missing its required unique-identifier attribute and value.OPF-041Fallback-style item with id "…" could not be found.OPF-049Item id "…" was not found in the manifest.
Sources
Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EpubCC.