Some ebooks contain non-native interactive or scripted elements—such as canvas, iframes, or widgets—that may not be supported by all reading systems. Providing fallback content prevents these elements from disappearing or rendering incorrectly.

Objectives

• Ensure access to information for users whose reading systems do not support specific technologies.
• Improve content accessibility for people with disabilities.

Implementation

• Provide fallback content for specific elements (including form interactions or external resources) so they can be rendered as a replacement if the reading system cannot display them.
• For EPUB files, link fallback content within the spine or within the specific elements they represent.

Control

• Check that the ebook remains readable and usable on legacy reading systems or when JavaScript is disabled.
• Verify that ‘object’ or ‘canvas’ elements are either not essential for understanding or have a text alternative.