EPUB Files — What are they?

EPUB is the most popular format for electronic reading. What makes it stand out?

In this article, we explore the structure of EPUB format.

Language to Know

Here are some terms that are useful to understand.

Metadata: Data that describes other data. For example, metadata might indicate that a block of text includes an author name, a title, a header, a list, an image, etc. In an accessible book, metadata can be used to describe elements to a blind reader.

XML: Is a text-based format used to represent and describe data. XML stands for Extensible Markup Language.

HTML: Is a text-based format used to represent content on a web page, primarily visual elements. HTML stands for Hypertext Markup Language.

XHTML: Similar to HTML but written using XML syntax rules. It has stricter error correction and is more universally compatible than its constituents. The most popular markup language for creating documents and web pages. XHTML stands for Extensible Hypertext Markup Language.

CSS: Is used to describe visual elements of style (colours, fonts, spacing, etc.) CSS stands for Cascading Style Sheet.

ZIP: A file format that compresses multiple files into a single location. 

What is an EPUB book?

An EPUB, or electronic publication, is a file format that is used for eBooks.

This type of file is the industry standard for eBook publishing. EPUBs are compatible with most devices, including e-readers, mobile devices, and computers. The file type supports metadata and allows for customizable features such as fonts and colours.

Although an EPUB is presented as a single file, it includes a set of interrelated resources in an unencrypted ZIP archive.

This means that, within the EPUB file, there exists several smaller files that help define the contents of the final EPUB.

These smaller files include HTML, CSS, images, and more.

How EPUB files increase accessibility

EPUB files have helped to increase accessibility in the publishing industry.

Audio playback features make EPUBs accessible to people who are blind, as the file functions both as an eBook and as an audiobook.

Text-to-speech (TTS) or overlay of audio and text can also be beneficial to people with cognitive disabilities such as dyslexia, as concurrent audio and text mediums can enhance understanding by connecting the sound of the words with the appearance of the text.  

EPUB books are customizable. Features like audio playback speed, text size, spacing and colour can be adjusted to one’s liking or need. Because they are based on XHTML, they are highly adaptable and reflowable.

EPUBs can be converted into different file types without distorting the content or appearance.

The incorporated navigation features enable all users to skip through pages or sections of an EPUB.

The New Standard: EPUB 3.0

While previous versions of EPUB were mostly for text-heavy, technical publications, the new EPUB 3 standard has the versatility to also display precise layouts or formatting (such as comic books or picture books).

Mathematical markup for formulas in digital formats is also supported, as well as linking within or between other EPUB books, and more standardization of EPUB structure and format for easier sharing and better functionality.

How to open EPUBs

EPUBs use the file extension “.epub”. They can be opened on desktop computers and mobile devices, including: iOS and Android phones and tablets, Barnes & Noble Nook, Kobo eReader and Amazon Kindle.

EPUBs can be read directly in a browser or through free apps such as Apple Books, Adobe Digital Editions, Thorium Reader, Dolphin Easy Reader, and EPUB File Reader.

Apps such as the Thorium Reader and Dolphin Easy Reader also include accessibility features such as support for high-contrast, customizable fonts (including dyslexic friendly fonts), colour themes, text size and TTS functions.

💡Did you know? CNIB Beyond Print helps organizations produce accessible EPUB 3 publications that conform to the latest version of the standard. Contact us to learn how.

Final Thoughts

The popularity of EPUBs has increased with the rise of accessible technology.

Accessible reading formats are now universally compatible; they can be read on almost any device.

These accessible features are integral to people who live with disabilities but are also beneficial to everyone.

However, all EPUBs are not inherently accessible. Learn how CNIB Beyond Print is working to change that.

Are you looking for books in accessible formats? View options for library services here.