What you need to know about EPUB 3

Now that the ink is dry on the final EPUB 3 specification from the International Digital Publishing Forum (IDPF), it seemed a good time to touch base with "What is EPUB 3?" (http://bit.ly/ufoRfx) author +Matt Garrish, who also was the chief editor of the EPUB 3 suite of specifications.

Our interview follows.

What advantages/challenges will EPUB 3 bring to the publishing table?

Matt Garrish: The biggest bang I see EPUB 3 bringing to the digital publishing world is undoubtedly the ease with which it will allow the creation of rich multimedia and interactive experiences. The ebook market has moved beyond the static two dimensions of the print page, and I don't think there's any stopping the march forward into uncharted digital territory.

We need to let go of the digital book — the one that doesn't have a print antecedent — and see where it will go, knowing full well that it won't translate back to print. I think that's still a scary idea to many people, but as the ebook market expands, growth in print-incompatible books is inevitable.

That's the biggest benefit I see this new revision bringing to the table, that it offers a clear path away from the print-centric ebook. EPUB is back ahead of the curve and will be both waiting as the format of choice as publishers embrace its new powers and doing its regular duties facilitating dual print/electronic production streams until then.

EPUB 3 alone isn't going to solve all the challenges that exist in digital content creation, but the new revision adds a lot of new weapons to your arsenal, making it that much easier to make high-quality ebooks. The specification is also so newly minted that trying to predict what challenges it will bring with it is a bit premature. Some we can all see coming, like audio and video size and location inside the container file or outside possibly affecting playback. But until the content gets developed, distributed and consumed, it's hard to say which of the many models that could emerge will prove best. I'm confident, though, that the IDPF will be providing guidance and instruction to producers as these kinds of issues develop, if not working to fix them in future revisions.

How do web standards affect EPUB 3?

Matt Garrish: The challenge creating a format like EPUB is navigating the unstable landscape that results when you have to build on top of moving targets. On the one hand, you have an HTML5 specification (http://bit.ly/syV5n8) that isn't finished. On the other, you have browser makers already implementing the standard and the features becoming generally available. Do you wait years and years until the specification is "signed, sealed and delivered," or do you jump in head first and take advantage of what exists now? The IDPF obviously opted to make the leap, so a good deal of the revision work went into circumscribing how to use the technologies in the state they're in so producers don't have to worry about future incompatibilities.

There's little to worry about in terms of using the new HTML5 elements that are available, like audio and video. But there's always concern when you have two agencies separately maintaining the same standard, as is the case right now with the W3C (http://www.w3.org/) and WHATWG (http://www.whatwg.org/). If browser cores start supporting custom new additions, as the WHATWG encourages, then suddenly you have a situation where reading systems may render features that are not allowed by the EPUB 3 specification. With the door open, how do you manage the standard and ensure interoperability between devices if people jump on a feature because they discover one platform supports it even though others possibly don't? The IDPF has plans for integrating experimental features using the epub:switch element (http://bit.ly/uhhn46), but it's not an easy problem to solve.

CSS3 (http://www.w3.org/TR/CSS/) is another unfinished suite of specifications, and its support in EPUB 3 was a little trickier than HTML5's. Many of the specifications are now reaching candidate recommendation status (i.e., they're at the point where they are considered stable) and are unlikely to change. But there were also needed properties that were not yet stable, which is why you'll find some prefixed with "-epub-" in the Content Documents specification (primarily from the CSS3 Speech and Text modules). We've taken a kind of snapshot in time of the standards they're defined in so we can use them and not worry if their behaviors change later, if their names are changed, or if they're dropped entirely. The IDPF was fortunate to have Elika Etemad (@fantasai) helping with the revision and coordinating our issues with the CSS groups, too.

Finally, standardized metadata expression languages (both publication-wide and inline) are still unstable within the W3C, with competing languages being proposed. The EPUB working group decided to postpone making a decision on inclusion of any of these until a future version when the landscape has stabilized. But even still, we've improved our metadata significantly with the ability now to add semantic tagging to XHTML5 documents — so you can indicate whether section elements represent parts or chapters or a prologue or epilogue, for example — and to refine metadata in the package document using ONIX code lists and other industry-standard controlled vocabularies.

Read the rest of this interview here: http://oreil.ly/vDtyNp

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