Back to Error DirectoryW3C EPUBCheck Standard
OBS-001.css-prefixed-valueRetailer Warning

the CSS prefixed value "resource"

the CSS prefixed value "resource"

Automated 1-Click Fix Ready

Fix all OBS-001.css-prefixed-value errors in your EPUB automatically

PreFlight checks for OBS-001.css-prefixed-value issues in memory and provides 1-click remediation during client-side packaging.

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What This Error Means in Plain English

EPUBCheck detected the CSS prefixed value "resource". Digital reading systems and bookstores require standard conformance to ensure compatibility across all reading apps.

Why Retailers & EAA Regulations Block This File

Automated book distributors (Apple Books, Amazon KDP, Kobo, and IngramSpark) run strict EPUBCheck validation on ingest and reject non-compliant files.

Technical Specification: W3C EPUBCheck rule OBS-001.css-prefixed-value: the CSS prefixed value "resource"

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule OBS-001.css-prefixed-value in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the OBS-001.css-prefixed-value specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.