Back to Error DirectoryW3C EPUBCheck Standard
RSC-029Critical Ingestion Error

Data URL is not allowed in this context.

Data URL is not allowed in this context.

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Fix all RSC-029 errors in your EPUB automatically

PreFlight checks for RSC-029 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 Data URL is not allowed in this context.. 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 RSC-029: Data URL is not allowed in this context.

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule RSC-029 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the RSC-029 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.