Knowledge · Rule

Invalid HTML/CSS construct (RSC-005 family)

Package Structure · E-RSC005

Definition

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.

Why

• 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.

Impact

May block submission on KDP when this rule fails.

Platforms

References

• EPUBCheck error codes (RSC-*)
• Amazon KDP: EPUB guidelines
• Cermify Rule Set kdp-epub-2026-07

Last updated · 2026-08-03

Related rules

• Severe HTML nesting errors
• Risky CSS for Kindle layout
• Non-UTF-8 encoded content file