Back to Error DirectoryW3C EPUBCheck Standard
HTM-010Critical Ingestion Error

Namespace "resource" is unusual for the prefix "epub".

Namespace "resource" is unusual for the prefix "epub".

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Fix all HTM-010 errors in your EPUB automatically

PreFlight checks for HTM-010 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 Namespace "resource" is unusual for the prefix "epub".. 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 HTM-010: Namespace "resource" is unusual for the prefix "epub".

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule HTM-010 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the HTM-010 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.