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HTM-056Critical Ingestion Error

Viewport metadata has no "resource" dimension (both "width" and "he...

Viewport metadata has no "resource" dimension (both "width" and "height" properties are required)

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Fix all HTM-056 errors in your EPUB automatically

PreFlight checks for HTM-056 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 Viewport metadata has no "resource" dimension (both "width" and "height" properties are required). 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-056: Viewport metadata has no "resource" dimension (both "width" and "height" properties are required)

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule HTM-056 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the HTM-056 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.