EPUB

EPUB is short for electronic publication and is a standard format for electronic books and was published in 2007 at the same time as the first EPUB readers appeared. The earlier EPUB versions were very limited in their functions and only allowed the display of text and images. However, newer versions of the EPUB standard also allow audio tracks, videos, formulas and interactive content to be displayed in electronic books - if the EPUB reader can handle these functions.

An EPUB file is essentially a zip archive that stores all the required files in a compressed format. As with websites, the content is displayed in HTML and formatted with CSS. Metadata such as book title, author and ISBN are stored in a central XML file. All assets in the zip archive such as covers, images and fonts must also be referenced there.

EPUB is now available in version 3.2, but some manufacturers of EPUB readers are very slow to support new versions. After the release of EPUB3 in 2011, it took almost another ten years for the format to be mastered by all common readers. For this reason, the practice in EPUB production has developed to optimize an EPUB to be as compatible as possible for all readers and to use modern EPUB features very sparingly. An audio book for reading learners in which the word being read is highlighted in color is possible with EPUB 3 - but it only runs on a few EPUB readers.

The accessibility of e‑books is also playing an increasingly important role, not least due to the ratification of the European Accessibility Act in the form of the Barrierefreiheitsstärkungsgesetz (BFSG) in Germany. The accessibility of EPUBs can be improved by a clear navigation, a correct heading hierarchy and language tagging, among many other small adjustments. EPUB3 offers many functions to improve accessibility, but the situation with screen readers for visually impaired people is hardly any different to that with EPUB readers. Screen readers are also lagging miles behind the development of the EPUB standard.

Despite these problems, EPUB has established itself as an open standard in the industry and has pushed back proprietary competitors such as Apple's iBook or Amazon's KF8. EPUB thus provides a certain degree of technological independence and gives publishers more control over their electronic products.