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EPUBCheck · XHTML content documents

EPUBCheck HTM-010: unusual epub namespace

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EPUBCheck HTM-010 is a usage message: “Namespace "…" is unusual for the prefix "epub".” The epub prefix is bound to an unusual namespace, so epub:type and other epub attributes may be ignored. Reading apps only recognise these attributes in the namespace http://www.idpf.org/2007/ops; with any other URI they are just unknown attributes. EPUBCheck reports it as a usage note and shows the namespace found.

The official message

Namespace "%1$s" is unusual for the prefix "epub".

Default severity
Usage. Informative only and hidden by default: it appears when EPUBCheck runs with -u (--usage). It does not make the EPUB invalid.
EPUBCheck version
5.4.0

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

Typical causes

  • A typo in the namespace declaration, such as a missing slash or an https URL.
  • A namespace copied from another vocabulary or an older draft.

How to fix it

  1. Open the file EPUBCheck names (the message gives the path, line and column) in a text or EPUB editor such as Sigil, or unzip the EPUB and open it there.
  2. Declare the prefix on the html element exactly as xmlns:epub="http://www.idpf.org/2007/ops".
  3. Keep the same declaration in every chapter so footnotes and other epub:type semantics work everywhere.
  4. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

When it's not this

If a namespace is declared and simply never used, that is HTM-044, not HTM-010.

Terms used here

Other HTM messages

  • HTM-009 The DOCTYPE provided is obsolete or irregular and can be removed.
  • HTM-011 Entity is undeclared.
  • HTM-007 Empty or whitespace-only value of attribute ssml:ph.
  • HTM-004 Irregular DOCTYPE: found "…", expected "…".
  • HTM-003 External entities are not allowed in EPUB v3 documents. External entity declaration found: ….
  • HTM-001 Any publication resource that is an XML-based media type must be a valid XML 1.0 document. XML version found: ….

Sources

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

FAQ

What does EPUBCheck HTM-010 mean?

EPUBCheck HTM-010 is a usage message: “Namespace "…" is unusual for the prefix "epub".” The epub prefix is bound to an unusual namespace, so epub:type and other epub attributes may be ignored. Reading apps only recognise these attributes in the namespace http://www.idpf.org/2007/ops; with any other URI they are just unknown attributes. EPUBCheck reports it as a usage note and shows the namespace found.

Is HTM-010 an error?

HTM-010 is reported as usage by default. Informative only and hidden by default: it appears when EPUBCheck runs with -u (--usage). It does not make the EPUB invalid.