EPUB 3 Specification: See the accessibility document.
Apple Books provides incredible opportunities to deliver high-quality reading experiences to everyone, including readers with accessibility needs.
Alternative text is an attribute of an image element contained within the HTML <img> element. Include the src (image source) attribute, the alt attribute, and an alt value in quotation marks that describes the image.
Alternative text should contain what you would put in prose if the image were not included, as shown in the following example:
<p>The hillside was covered in poppies. <img src="images/flowers.jpeg"alt="The poppies are red, orange, and yellow, and a winding path leads to a house."/>A dog was asleep on the porch.</p>The following attributes are not acceptable:
alt="none"
alt="nothing"
alt="image"
alt="page 3"
Don’t use the word "image" in the alt text. With VoiceOver, the alternative text alt="image of poppies" is typically spoken as "image of poppies, image."
When the image is decorative and does not have any content or meaning, use the empty attribute alt="" to suppress irrelevant information for VoiceOver users.
Navigational structure is a key component of EPUB 3 files. EPUB structure helps readers with accessibility needs to easily navigate through the book. In Apple Books, navigation defines where a book starts and how samples are generated among other features.
See Navigation Document.
Core HTML markup does not always differentiate common publishing structures within the text. Instead, CSS styling provides visual differentiation and helps the reader identify those structures.
The ARIA role attribute, available in EPUB 3, can augment HTML for those who use assistive technologies. ARIA roles are defined in the W3C WAI-ARIA specification.
Mathematical Markup Language (MathML) is a powerful XML-based language in EPUB 3 that represents math notations both in the visual layer and in description through assistive technologies.
For information on using MathML in EPUB, see the W3C math homepage. For recommendations on implementation and the full specification, see the Math Working Group publications.
In complex elements, such as charts, text, or other graphical elements, color should not be the sole means of visual distinction or of conveying information. To help low vision and colorblind users comprehend the given information, provide other cues like text labels, shapes, patterns, or other differentiation.
When designing a fixed layout book, ensure a contrast ratio of 4.5:1 at minimum—or 3:1 for large/heading text—against the background color.