Back to Error DirectoryW3C EPUBCheck Standard
HTM-051Critical Ingestion Error

Found Microdata semantic enrichments but no RDFa. EDUPUB recommends...

Found Microdata semantic enrichments but no RDFa. EDUPUB recommends using RDFa Lite.

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Fix all HTM-051 errors in your EPUB automatically

PreFlight checks for HTM-051 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 Found Microdata semantic enrichments but no RDFa. EDUPUB recommends using RDFa Lite.. 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-051: Found Microdata semantic enrichments but no RDFa. EDUPUB recommends using RDFa Lite.

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule HTM-051 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the HTM-051 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.