EpubCCEPUBCheck PKG-017: uncommon file extension
Updated:
EPUBCheck PKG-017 is a warning message: “Uncommon EPUB file extension.” The file does not end in .epub, so some reading apps and stores may not recognise it. EPUBCheck reports the same text, "Uncommon EPUB file extension", as PKG-017 (a warning) and as PKG-024 (a usage message); the cause and the fix are the same.
The official message
Uncommon EPUB file extension.
EPUBCheck's suggestion: For maximum compatibility, use ".epub".
- Default severity
- Warning. The EPUB is still valid, but something is likely to cause problems in some reading apps. EPUBCheck exits with 0 unless you pass --failonwarnings.
- EPUBCheck version
- 5.4.0
Typical causes
- A file saved with another extension, such as .zip or .epub3, or with none.
- A double extension added by a download or email client, such as book.epub.zip.
- PKG-024: the same message at usage level, shown when EPUBCheck runs with -u (--usage).
How to fix it
- Rename the file to end in .epub.
- Nothing inside the EPUB needs to change: the content, the mimetype file and the package document stay as they are.
- If a script or service produces the file, fix the extension there so the next build is right.
When it's not this
If the extension is .epub but in uppercase, the message is PKG-016.
Also reported as
PKG-024(usage): Uncommon EPUB file extension.
Terms used here
Other PKG messages
PKG-016Use only lowercase characters for the EPUB file extension for maximum compatibility.PKG-018The EPUB file could not be found.PKG-014The EPUB contains empty directory "…".PKG-020OPF file "…" could not be found.PKG-021Corrupted image file encountered.PKG-012The file name "…" contains non-ASCII characters, which might create interoperability issues with older reading systems.
Sources
Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EpubCC.