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EPUBCheck · XHTML content documents

EPUBCheck HTM_061: invalid data-* attribute

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EPUBCheck HTM_061 is an error message: “"…" is not a valid custom data attribute (it must have at least one character after the hyphen, be XML-compatible, and not contain ASCII uppercase letters).” A data-* attribute name is not valid. A custom data attribute needs at least one character after the hyphen, no uppercase ASCII letters and only characters allowed in XML names.

The official message

"%1$s" is not a valid custom data attribute (it must have at least one character after the hyphen, be XML-compatible, and not contain ASCII uppercase letters).

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

EPUBCheck prints this ID with an underscore instead of a hyphen; this page uses the ID exactly as EPUBCheck reports it.

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

Typical causes

  • Names such as data-, data-Page or data-x:y.
  • Attributes generated from a script or a design tool that keeps camelCase names.

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. Rename the attribute in lowercase, for example data-page instead of data-Page.
  3. If a script or stylesheet reads the attribute, update it to the new name too.
  4. Remove the attribute if nothing in the book uses it.
  5. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

When it's not this

If the attribute is prefixed with a namespace (such as ibooks:something), the rules are those of custom attributes, reported as HTM_054.

Terms used here

Other HTM messages

  • HTM_060b EPUB reading systems must ignore viewport meta elements in reflowable documents; viewport declaration "…" will be ignored.
  • HTM_062 SVG "xlink:href" attribute is deprecated; an "href" attribute should be used instead.
  • HTM_059 Viewport "…" property must not be defined more than once, but found values […].
  • HTM_058 HTML documents must be encoded in UTF-8, but UTF-16 was detected.
  • HTM_057 Viewport "…" value must be a positive number or the keyword "device-…"
  • HTM_056 Viewport metadata has no "…" dimension (both "width" and "height" properties are required)

Sources

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

FAQ

What does EPUBCheck HTM_061 mean?

EPUBCheck HTM_061 is an error message: “"…" is not a valid custom data attribute (it must have at least one character after the hyphen, be XML-compatible, and not contain ASCII uppercase letters).” A data-* attribute name is not valid. A custom data attribute needs at least one character after the hyphen, no uppercase ASCII letters and only characters allowed in XML names.

Is HTM_061 an error?

HTM_061 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.