Back to Error DirectoryW3C EPUBCheck Standard
CSS-015Retailer Warning

Alternative style sheets must have a title.

Alternative style sheets must have a title.

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PreFlight checks for CSS-015 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 Alternative style sheets must have a title.. 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 CSS-015: Alternative style sheets must have a title.

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule CSS-015 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the CSS-015 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.