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EPUBCheck · Package document (OPF)

OPF-021

Updated:

EPUBCheck OPF-021 is a warning message: “Use of non-registered URI scheme type in href: "…".” An href uses a URI scheme that is not registered (not http, https, mailto and other standard schemes).

The official message

Use of non-registered URI scheme type in href: "%1$s".

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

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

Typical causes

  • A typo in the scheme, such as htp:// or http//, or an app-specific scheme.

How to fix it

  • Correct the scheme, or remove the link if it only works in one app.

Terms used here

Other OPF messages

  • OPF-018 The "remote-resources" property was declared in the Package Document, but no reference to remote resources has been found.
  • OPF-017 The attribute "full-path" on element "rootfile" must not be empty.
  • OPF-025 Property value list "…" is not allowed, only one value must be specified.
  • OPF-016 The element "rootfile" is missing its required attribute "full-path".
  • OPF-026 Found malformed property value: "…".
  • OPF-015 The property "…" should not be declared in the OPF file.

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

FAQ

What does EPUBCheck OPF-021 mean?

EPUBCheck OPF-021 is a warning message: “Use of non-registered URI scheme type in href: "…".” An href uses a URI scheme that is not registered (not http, https, mailto and other standard schemes).

Is OPF-021 an error?

OPF-021 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.