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EPUBCheck · Package document (OPF)

OPF-004

Updated:

EPUBCheck OPF-004 is a warning message: “Invalid prefix declaration: leading or trailing whitespace is not allowed.” A prefix declaration in the package document has leading or trailing whitespace.

The official message

Invalid prefix declaration: leading or trailing whitespace is not allowed.

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

  • Spaces or line breaks at the start or end of the prefix attribute value.
  • Hand-edited or tool-generated package documents that write the prefix attribute with the wrong separators.

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/". Remove the whitespace at the start and end of the value.
  • Reserved prefixes such as dcterms, rendition and schema need no declaration at all.

Terms used here

Other OPF messages

  • OPF-004a Invalid prefix declaration: found empty prefix.
  • OPF-004b Invalid prefix "…": must be a valid non-colonized name (aka "NCName").
  • OPF-004c Invalid prefix declaration: prefix "…" must be immediately followed by a colon character (":").
  • OPF-004d Invalid prefix declaration: prefix "…" must be separated by its URI with a space.
  • OPF-004e Invalid prefix declaration: found illegal whitespace between prefix and URI.
  • OPF-004f Invalid prefix declaration: found illegal whitespace between prefix mappings.

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

FAQ

What does EPUBCheck OPF-004 mean?

EPUBCheck OPF-004 is a warning message: “Invalid prefix declaration: leading or trailing whitespace is not allowed.” A prefix declaration in the package document has leading or trailing whitespace.

Is OPF-004 an error?

OPF-004 is reported as warning by default. The EPUB is still valid, but something is likely to cause problems in some reading apps. EPUBCheck exits with 0 unless you pass --failonwarnings.