Package Structure · E-RSC005
Invalid HTML/CSS construct (RSC-005 family)
Your EPUB contains HTML or CSS that KDP's validator flags as invalid (commonly reported as RSC-005). This usually comes from exporters like Canva or Google Docs leaving behind unsupported attributes or unclosed tags.
Error: Invalid HTML/CSS construct (RSC-005 family)
Category: Package Structure
Severity: error
Auto Repair: Supported
Rule ID: E-RSC005
Affected: KDP=reject, Apple=reject, Google=reject, Kobo=reject
Check this automatically with Cermify
Why this happens
- Word / Google Docs / Canva export left proprietary or obsolete attributes (e.g. align, face, or vendor data-*).
- Unclosed or mismatched tags after manual edits or merge of chapter files.
- CSS using constructs Kindle's pipeline rejects (invalid selectors, unknown at-rules, broken declarations).
- XHTML served as HTML5 syntax (or the reverse) so the document is not well-formed XML.
How platforms treat it
| Platform | Result |
|---|
| KDP | reject |
| Apple Books | reject |
| Google Play | reject |
| Kobo | reject |
How Cermify detects it
- Unpack the EPUB and run epubcheck (or KDP Previewer) against content documents.
- Collect RSC-005 / well-formedness messages with file path and line.
- Inspect the cited element or CSS rule for unsupported attributes, bad nesting, or invalid syntax.
- Confirm the content document is XML-well-formed XHTML when required by the EPUB version.
Automatic repair
Cermify can strip or rewrite many known RSC-005 offenders (unsupported attributes, common unclosed tags, selected CSS cleanups) and recheck. Rare or novel constructs may still need a manual pass.
Manual fix
- Open the file named in the validator message (usually a .xhtml / .html chapter or stylesheet).
- Fix well-formedness first: close tags, escape & as &, ensure a single root element.
- Remove or replace attributes and CSS that epubcheck rejects; prefer EPUB-safe CSS.
- Repackage the EPUB and re-run epubcheck / KDP upload until RSC-005 is gone.
Examples
Unsupported align / MSO attributes and an unescaped ampersand commonly trigger RSC-005.
Incorrect
<p align="center" style="mso-spacerun: yes">Hello & welcome</p>
Correct
<p class="center">Hello & welcome</p>
FAQ
Is every RSC-005 message the same problem?
No. RSC-005 is a family of epubcheck reports about invalid markup or CSS. The fix depends on the cited line—attribute, nesting, encoding, or stylesheet syntax.
Will Kindle still open the book if I ignore it?
KDP typically rejects the upload when RSC-005 (or equivalent) remains. Do not rely on device preview alone; clear the validator errors first.
Why do Canva or Docs exports fail more often?
Those tools optimize for web or print layout, not EPUB XHTML. They often emit proprietary attributes and incomplete markup that epubcheck flags.
Related errors
References