A common question I hear is whether EPUB3 is useless above and beyond HTML5. Why not just eliminate EPUB and use plain HTML5?

EPUB3 does bring new things to the table that HTML5 does not provide.

I see standards and technologies like ecosystems that respond to the challenges that are thrown at them. Before eBook systems, the web only had infrastructure for individual web pages that were either documents or application-like. HTML before HTML5 didn't even help much with applications, except for basic forms, so HTML5 provided features to help with this area (offline web apps, the canvas tag, etc.).

There has never been evolutionary pressure on HTML to have better long form reading for artifacts akin to eBooks, so it never really provided the facilities to help with this.

The key limitation of HTML5 is it never evolved a way to talk about anything beyond single web pages; it provides markup for individual pages, but somehow forgot to provide a way to talk about collections of pages as a unit. You can think of an eBook as simply a bundle of web pages.

In addition, HTML in general never provided the following:

• The ability to define what role the web pages in a bundle play. What order should they be read in? Is one of them the introduction? Are some of them out of the ordinary flow (i.e. are they appendices)?
• The ability to bundle a group of web pages together, along with all of their media resources (images, CSS, etc.), so they can be downloaded (‘purchased’) together efficiently, like PDF does.
• The ability to provide annotation facilities across a collection of web pages (footnotes, glossaries, etc).

These are all the key features we associate with eBooks. EPUB3 provides solutions for each of these pieces:

• The ability to group web pages together into collections that today we call eBooks (In the long run, I think what we call eBooks will simply be seen as bundles of web pages; we might end up calling these eBooks or adopting some other future name.)
• The ability efficiently bundle all of them together, along with their media assets, into a ZIP file.
• A manifest file detailing the reading order and available files.
• Common ways to mark up structural aspects of eBooks and facilities like footnotes, glossaries, etc.

None of these features come out of the box with HTML5; you either need EPUB3 for them or you have to roll your own (incompatible) personal markup above HTML5.

In the long run, I see many of the pieces of EPUB3 simply getting absorbed into a future HTML; the new name of HTML5 is The Living Standard, so it's designed exactly to absorb useful bits of functionality like this. Things like footnotes, glossaries, web pages as ZIP files, and bundles of associated web pages are all generally useful to the open web as eBooks and the web continue merging.

Unfortunately, EPUB3 has some serious problems when it comes to making it compatible with the broader HTML5 web that need to be fixed. I'll detail these in a future blog post.

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