Category: 7.5 Update to EPUB3

DigitalAladore 1.5, EPUB3 Edition!

Is DigitalAladore 1.0 looking crummy on your ultra high def 10 inch tablet screen?

Well, give DigitalAladore 1.5 a try! Following the workflow outlined in previous posts, I generated an Aladore EPUB3 edition. The images are much bigger and the CSS is slightly tweaked with larger screens in mind. Personally, I still find reading ebooks on tablets a bit unsatisfying, slightly too big and bright. But I think this version will look pretty good! However, at over 9MB it might be slow to load on your e-ink reader.

So with out further ado, you can find the new EPUB3 at Internet Archive,

DigitalAladore 1.5: Aladore, by Henry Newbolt (1914, epub3), https://archive.org/details/AladoreHenryNewbolt3

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Thoughts About EPUB3

When I first started looking into the EPUB3 specs, I was excited by the possibilities of a more powerful ebook format. Just think of all the neat things you can create with simple CSS and JS! I imagined creating little “epub apps” like a calculator or timer. It would be a neat way to add functionality to very simple devices such as the Sony Reader. I created a few test versions, however these demos often worked in Calibre’s built in reader, but were not functional with any actual ereaders.

Of course, the point would be to go beyond silly little apps and add some interesting and valuable extensions to the ebook, such as text collation or visualizations. Simple adjustable collation tools could be embedded so that the reader could query the text while reading. Some of this functionality has been built into the reading apps on some devices, such as Kindle X-Ray. Simple interactive elements would be useful for textbooks and manuals to make information delivery more interesting. Imagine something like Jupyter Notebook, which can run embedded Python code.

Unfortunately, there just isn’t good support for the advanced features of EPUB3 in an open and flexible way.  As I mentioned in a previous post, device makers only seem interested in the possibilities of further limiting users with tougher DRM, rather than enabling new possibilities. In the ideal world we could combine the open format with open hardware and software!

Remove the NCX

Interested in minuet EPUB intricacies? Good, you are in for a treat!

One of the steps I mentioned for going from EPUB2 to EPUB3 is removing the toc.ncx file. This is actually a some what involved step (that is probably unnecessary) so I thought I would expand on it a bit.  It also gives you a chance to poke around EPUB innards…

The NCX, i.e. “Navigation Center eXtended” was a feature to enhance navigation and accessibility based on the DAISY/NISO Standard. It was a required Spine element in EPUB2.  However, the EPUB 3.0.1 spec that tells you the NCX is Superseded. Instead you are required to include an EPUB Navigation Document (i.e. nav.xhtml) that makes use of the HTML5 nav element. Basically you need to set up a <nav>, with <ol> inside, with <li> that have <a> relative links to parts of the ebook.

Since this file is a valid HTML document, it can be easily rendered by the reading device. Thus the new navigation file can serve both as a human and machine readable TOC.  You can write the table of contents once in <nav>, use it at the beginning of the book (for people) and for the device to understand the reading order of the digital files to provide extended navigation.

So in EPUB3 you need a Nav doc, but do you need to get rid of NCX? No, not really… NCX Superseded says that we “MAY” include the NCX since it will not interfere with anything, “but EPUB 3 Reading Systems must ignore the NCX.” I.e. older devices will keep looking for NCX, but newer ones will definitely not.

So we have an EPUB2, we create a new Nav based TOC, the question is NCX to keep or not to keep… I really don’t have a good answer.  It seems there is no reason to not keep it?

But if you want to get rid of it, building a Pure EPUB3, its more complicated than just deleting one file. Here’s what you need to do:

  • Unzip your EPUB (it is probably already unzipped if you are monkeying around with the EPUB2 to 3 transition), navigate to the OEBPS directory.
  • Delete the toc.ncx.
  • Open the content.opf file in a text editor. This is an XML that defines the ebook.
  • Look for the <manifest> element and find an <item> listing for the NCX (easiest just to search for “.ncx”).  It should look something like this: <item href="toc.ncx" id="ncx" media-type="application/x-dtbncx+xml"/>. Delete it!
  • Find the <spine> element. It should have a TOC attribute that looks like this: <spine toc="ncx">. Delete the whole attribute as it is optional in EPUB3, leaving <spine>.
  • Save your cleansed content.opf!

ncxLet me know what you decide!