EpubCCEPUBCheck OPF-055: empty EPUB 2 metadata tag
Updated:
EPUBCheck OPF-055 is a warning message: “… tag is empty.” A metadata element in an EPUB 2 package document is empty, and EPUBCheck names it. Empty metadata gives reading apps and stores nothing to show, so it is reported as a warning.
The official message
%1$s tag is empty.
- Default severity
- Warning. The EPUB is still valid, but something is likely to cause problems in some reading apps. EPUBCheck exits with 0 unless you pass --failonwarnings.
- EPUBCheck version
- 5.4.0
%1$s, %2$s… are filled in with the file, value or element EPUBCheck found.
Typical causes
- An empty dc:title, dc:identifier or dc:date left in a template.
- A field exported from a catalogue where the value was blank.
- A value removed by hand without removing its element.
How to fix it
- Find the element EPUBCheck names in the metadata section.
- Fill it with a real value.
- If you have no value for an optional element, delete it; required ones (title, identifier, language) must be filled.
When it's not this
In EPUB 3 empty metadata is caught by the schema and reported as RSC-005; other empty Dublin Core elements in EPUB 2 are OPF-072.
Terms used here
Other OPF messages
OPF-054Date value "…" is not valid as per http://www.w3.org/TR/NOTE-datetime:….OPF-053Date value "…" does not follow recommended syntax as per http://www.w3.org/TR/NOTE-datetime:….OPF-050TOC attribute references resource with non-NCX mime type; "application/x-dtbncx+xml" is expected.OPF-060Duplicate entry in the ZIP file: "…" (file names must be unique after Unicode canonical normalization and full case folding).OPF-049Item id "…" was not found in the manifest.OPF-048Package tag is missing its required unique-identifier attribute and value.
Sources
Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EpubCC.