The Publishing Maintenance Working Group at W3C has been quietly working on yet another update for the EPUB3 standard, and we’re excited to share what we have been up to. Our goal is to not only maintain the EPUB standard, but do our best to keep it in line with the needs of industry, and this update does exactly that.
Before we get into the updates, we want to remind everyone that our first priority is backwards compatibility, meaning that all updates to EPUB3 must not render previously created files inoperable. Your existing books do not need to change, if they conform to previous versions of EPUB, they will conform to EPUB 3.4. Content you create today will automatically conform to EPUB 3.4 if it validates.
EPUB 3.4 includes the core specification, the reading systems specification, and an update to EPUB Accessibility 1.2. We are currently in the candidate stage of the W3C publishing process. That means we are currently testing the specification, seeking feedback from implementers, and ensuring the revisions are solid before final publication. If you are a reading system or tool developer, we would love your input. To test the specification, you can find more information on the testing website.
Roll layout demo from W3C Member Kadokawa on their Publus reader
Introducing roll layouts
One of the most exciting trends in publishing over the last few years globally has been the astounding rise of “webtoons”, a popular comic format that originated in South Korea. Webtoons are typically episodic digital comics that are read vertically as opposed to horizontally like manga or western comics. They were designed to be read easily on smart phones and are laid out in one long, vertical strip of images. Up until now, webtoons were confined to specialty reading applications or websites, because there was no support for them in a format like EPUB. In EPUB 3.4, we are changing that.
We have added a new rendition:layout value: roll. Roll layouts indicate to the reading system that the content should be rendered where each spine item fills the width of the viewport and are displayed sequentially without gaps between the items. Roll layouts will only work with fixed layout documents, but cannot be controlled by other rendering options for fixed layout such as rendition:page-spread or spine level layout overrides such as rendition:layout-reflowable. Roll layouts inherit the same accessibility challenges as fixed layout EPUBs, and we recommend reviewing our documentation for fixed layout accessibility.
A 40-second demo of the roll layout feature in EPUB, provided by W3C Member Kadokawa on their Publus reader
What else has changed in EPUB 3.4?
As with previous updates to the standard, we have focused on making the specifications easier to understand, clearer, and in line with industry practices. This includes adding new content types or codecs for images, audio and video such as AVIF, JPEG XL, and OPUS; refining accessibility metadata to ensure the best information for users; and adding new accessibility metadata fields for contact emails. As with previous revisions, we also did some housekeeping.
On October 11, EPUB 3 will turn 15 years old, and much has changed in that time. With a decade and a half of history, we can look back at what has worked and what has not. In EPUB 3.4, you’ll see a number of features have been moved to what we call “obsolete” features, classified by either “outdated” or “deprecated”.
Outdated features
Outdated features are legacy features that authors and developers are discouraged from using in new work, but reading systems must continue to support. This category ensures existing EPUB files remain valid and readable without encouraging outdated practices in modern content.
One feature that has been marked outdated in EPUB 3.4 is font obfuscation, which relies on encryption features that are no longer recommended. We encourage EPUB creators to use modern font formats like WOFF2 instead. You can find more information on what has been determined to be outdated, and potential alternatives to those features, in the “Outdated features” section of the specification.
Deprecated features
A deprecated feature is one that has little to no support in reading systems or EPUB publications. When a feature is deprecated, we strongly recommend not using it, and EPUBCheck will warn the user.
An example of a deprecated feature is the XHTML extension element switch, which allowed for the conditional insertion of new content, but is no longer recommended in favor of more modern techniques. You can find more information on what has been deprecated and potential alternatives to those deprecated features in the “Deprecated features” section of the specification.
Update to EPUBCheck
EPUBCheck v5.4.0 has been released to include the requirements for EPUB 3.4, meaning that EPUB creators can now check their files for conformance against the latest version of the specification. As a reminder, if the EPUB validates, it conforms, so no major changes are needed for EPUB creators to meet the new version of the specification.
In addition to support for the new roll layout type, EPUBCheck v5.4.0 also checks for newly added content types including AVIF and JPEG XL, as well as the OPUS and AAC codecs for MP4. EPUBCheck also now supports the a11y:contactEmail metadata property and the doc-pageheader and doc-pagefooter DPUB ARIA roles.
The remaining changes to EPUBCheck for EPUB 3.4 cover a number of small changes made in the specification to address outdated or deprecated features. These features will no longer be recommended in the specification as we see low support levels or they have been superseded by newer features or practices. EPUBCheck will now offer notices to users that these features are present and are outdated. This means that there is a risk they may not work in all reading systems, and if used we recommend testing or transitioning to the supported feature. Examples include content fallbacks, CSS prefixed properties, and old OPF2 elements like guide and NCX.
What’s next for EPUB 3
As we await the completion of the testing phase for EPUB 3.4, we are hard at work on building the upcoming EPUB Annotations specification for improving the interoperability of EPUB annotations. We are also looking at future improvements for EPUB 3 and beyond as we begin the process of developing the new charter for the Publishing Maintenance Working Group, or outline of what we plan to work on.
If there are features or areas you feel we are not addressing, we want to know! We are constantly looking for input on what needs to be done to support the publishing industry, and your input is essential. We encourage anyone with feedback or questions to email the Publishing Maintenance Working Group at public-pm-wg@w3.org. If you would like to join us in the work of Digital Publishing standards, please become a W3C Member, or contact the W3C Membership Team at membership@w3.org for information on joining.