EpubCCEPUBCheck OPF-021: unregistered URI scheme
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, unlike http, https or mailto. Reading apps may not know what to do with an unregistered scheme, so the link can fail silently.
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//.
- An app-specific scheme that only works in one program, such as a link meant for a particular reader.
- A local file path (C:\…) written where a URL was expected.
How to fix it
- Find the href EPUBCheck names.
- Correct the scheme to a standard one (https, http, mailto…) if it is a typo.
- If the link only works in one app or on one computer, remove it or replace it with a web address.
When it's not this
If the link points to a file inside the EPUB that does not exist, that is RSC-007.
Terms used here
Other OPF messages
OPF-018The "remote-resources" property was declared in the Package Document, but no reference to remote resources has been found.OPF-018bThe "remote-resources" property was declared in the Package Document, but no reference to remote resources has been found; please check scripted content to make sure the property is legit.OPF-017The attribute "full-path" on element "rootfile" must not be empty.OPF-025Property value list "…" is not allowed, only one value must be specified.OPF-016The element "rootfile" is missing its required attribute "full-path".OPF-026Found malformed property value: "…".
Sources
Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EpubCC.