Back to Error DirectoryW3C EPUBCheck Standard
HTM-054Critical Ingestion Error

Custom attribute namespace ("resource") must not include the string...

Custom attribute namespace ("resource") must not include the string "resource" in its domain.

Automated 1-Click Fix Ready

Fix all HTM-054 errors in your EPUB automatically

PreFlight checks for HTM-054 issues in memory and provides 1-click remediation during client-side packaging.

Scan & Fix Now

What This Error Means in Plain English

EPUBCheck detected Custom attribute namespace ("resource") must not include the string "resource" in its domain.. 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-054: Custom attribute namespace ("resource") must not include the string "resource" in its domain.

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule HTM-054 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the HTM-054 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.