Thursday, July 25, 2013

Straw-Man Spec

Consider this a straw-man outline of the spec, as I envision it.

What’s inside?

  1. An e0 file has file extension .e0
  2. An e0 is a zipped folder which contains an index.html file
  3. index.html is an HTML5 content file, and shall contain at least one nav element, unless index.html is the only HTML5 content file.
  4. By default, the first nav element in index.html serves as both primary navigation (hereafter referred to as "toc") and as an indication of the reading order (hereafter referred to as "spine", in keeping with EPUB terminology). If an li element in the first nav in index.html is not otherwise marked, the referenced file should appear in both the reading system's primary navigation interface, and be part of the linear reading order.
  5. If a file should be omitted from toc, but remain in the spine, use the hidden attribute on the list item. Among other things, this means that, in most cases, a web browser (that knows nothing of e0) opening up index.html will do the right thing.
  6. If a file should be omitted from the spine, but remain in the primary toc, add role="toc" to the list item. We’re hoping this is quite rare.
  7. If a file should be omitted from both the spine and toc, it should not appear in nav in index.html. There’s no obligation for all content documents to appear here.
  8. An e0 reading system should not open index.html directly, but display the first content file referenced in the first nav in index.html (unless there's no nav in index.html). Ideally this first content file would be the book cover.
  9. Document metadata lives in index.html. Section metadata can live in the individual content files. The metadata vocabulary is being discussed; for now use meta in the html head.
  10. If there is a cover image, it should be referenced in index.html via link rel="cover"
  11. Either the HTML or the XHTML serialization of HTML5 is allowed.
  12. MathML and SVG in HTML5 documents are allowed.

What’s not?

  1. There’s no mimetype file, META-INF folder, or container.xml file. Rather than using container.xml to point to the “root,” the reading system just needs to find index.html.
  2. There’s no special method of zipping
  3. There’s no package file.  index.html serves many of the same purposes, but tries to avoid duplication and non-HTML vocabularies. 
  4. There’s no manifest. The computer can figure out what files are in the zip, and can probably figure out what kinds of files they are.
  5. e0 does not have a CSS profile. 
  6. Landmarks and guides are omitted. We already know where the toc and cover are. If you want the reader to begin reading at a specific place, put that place at the beginning of the book!


  1. Simplicity
  2. Avoid duplication
  3. Use HTML vocabularies wherever possible
  4. Make life easier for the content creator, even if that makes life harder for the reading system developer

Monday, July 15, 2013

e0 Incarnate, and a Note on Navigation

e0 Incarnate

The first e0 file is, of course, Moby-Dick, available for download here. Those of you who have followed the conversation will notice that it is much like the original proposal, with one exception.

A Note on Navigation, Reading Order, and index.html

The major change is the handling of the primary navigation in index.html. On the mailing list, we reached a consensus that the role attribute would be the primary method of adding semantics to HTML5 elements, thus avoiding namespaced attributes (epub:type), HTML5 data- attributes, and other such horrors.

The primary vocabulary for @role will be the EPUB3 Structural Semantics Vocabulary, extended as needed. How can this help with index.html? I'm hoping this will allow us to use a single nav element to function as both nav and spine.

For the first nav element in index.html, we will define the default behaviour to be as if every element was role="toc spine". This means:
  1. The element appears in the default navigation structure ("toc")
  2. The element appears in the document's linear reading order ("spine"), as in EPUB's linear="yes".
So if an element is marked as role="toc" it means it does appear in default nav, but is not in the default linear reading order. If an element is marked as role="spine" it appears in the linear reading order, but does not appear in default navigation. If you don't want either function, just leave the section out of index.html//nav[1]. There is no obligation to list all content documents in the e0 folder.

One can choose to hide the default navigation from displaying on the index.html page by using the hidden attribute.