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EPUBCheck · Package document (OPF)

OPF-028

Updated:

EPUBCheck OPF-028 is an error message: “Undeclared prefix: "…".” A property uses a prefix that is not declared in the package document's prefix attribute.

The official message

Undeclared prefix: "%1$s".

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

%1$s, %2$s… are filled in with the file, value or element EPUBCheck found.

Typical causes

  • Vendor properties such as ibooks:version used without declaring the ibooks prefix.

How to fix it

  • The prefix attribute on the package element maps short prefixes to vocabulary URIs, as space-separated pairs like prefix="ibooks: http://vocabulary.itunes.apple.com/rdf/ibooks/vocabulary-extensions-1.0/". Add the mapping for the prefix, or remove the property.

Terms used here

Other OPF messages

  • OPF-027 Undefined property: "…".
  • OPF-029 The file "…" does not appear to match the media type …, as specified in the OPF file.
  • OPF-026 Found malformed property value: "…".
  • OPF-030 The unique-identifier "…" was not found.
  • OPF-025 Property value list "…" is not allowed, only one value must be specified.
  • OPF-031 File listed in reference element in guide was not declared in OPF manifest: ….

Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EPUBLab.

FAQ

What does EPUBCheck OPF-028 mean?

EPUBCheck OPF-028 is an error message: “Undeclared prefix: "…".” A property uses a prefix that is not declared in the package document's prefix attribute.

Is OPF-028 an error?

OPF-028 is reported as error by default. 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.