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EPUBCheck · Resources and references

RSC-020

Updated:

EPUBCheck RSC-020 is an error message: “"…" is not a valid URL (…).” A URL in the EPUB is not syntactically valid.

The official message

"%1$s" is not a valid URL (%2$s)

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

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

Typical causes

  • Unencoded spaces or other characters that must be percent-encoded in a URL.
  • Backslashes used as path separators (a Windows habit) instead of forward slashes.

How to fix it

  • Percent-encode spaces as %20 and other reserved characters, use forward slashes, or rename the file so its URL needs no encoding.

Terms used here

Other RSC messages

  • RSC-017 Warning while parsing file: …
  • RSC-016 Fatal Error while parsing file: …
  • RSC-015 A fragment identifier is required for svg use tag references.
  • RSC-026 URL "…" leaks outside the container (it is not a valid-relative-ocf-URL-with-fragment string)
  • RSC-013 Fragment identifier is used in a reference to a stylesheet resource.
  • RSC-027 XML document is encoded in UTF-16. It should be encoded in UTF-8 instead.

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

FAQ

What does EPUBCheck RSC-020 mean?

EPUBCheck RSC-020 is an error message: “"…" is not a valid URL (…).” A URL in the EPUB is not syntactically valid.

Is RSC-020 an error?

RSC-020 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.