Older reading systems may not support EPUB 3. By ensuring backward compatibility with EPUB 2, publishers ensure their ebooks remain readable for users with legacy devices.

Objectives

• Ensure readability on legacy reading systems.

Implementation

• Use EPUB 2 cover metadata.
• Include a Table of Contents in toc.ncx format.
• Add EPUB 2 guides to mirror EPUB 3 landmarks.
• Apply CSS rules to HTML5 elements to ensure they display correctly on reading systems that do not support HTML5.
• Place styles for specific screen sizes or use cases, such as print or audio rendering (media queries), in a separate CSS file.

Control

• Check for the presence of cover metadata in the OPF file.
• Verify that a toc.ncx file is present.
• Check for a guide section in the OPF file.
• Verify that CSS rules are provided for HTML5 elements (e.g., article, aside, details, figure, figcaption, footer, header, nav, section).
• Check that CSS files are separated if the layout relies on media queries.