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EPUBCheck · XHTML content documents

HTM_061

Updated:

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: it needs at least one character after the hyphen, no uppercase ASCII letters and XML-compatible characters.

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.

How to fix it

  • Rename the attribute in lowercase, for example data-page.

Terms used here

Other HTM messages

  • HTM_060a EPUB reading systems must ignore secondary viewport meta elements in fixed-layout documents; viewport declaration "…" will be ignored.
  • 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_063 SVG "xlink:href" attribute value ("…") should be equal to the "href" attribute value ("…").
  • HTM_057 Viewport "…" value must be a positive number or the keyword "device-…"
  • HTM_055 The "…" element should not be used (discouraged construct)

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

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: it needs at least one character after the hyphen, no uppercase ASCII letters and XML-compatible characters.

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.