- An e0 file has file extension .e0
- An e0 is a zipped folder which contains an index.html file
- index.html is an HTML5 content file, and shall contain at least one nav element, unless index.html is the only HTML5 content file.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- If there is a cover image, it should be referenced in index.html via link rel="cover"
- Either the HTML or the XHTML serialization of HTML5 is allowed.
- MathML and SVG in HTML5 documents are allowed.
- 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.
- There’s no special method of zipping
- There’s no package file. index.html serves many of the same purposes, but tries to avoid duplication and non-HTML vocabularies.
- 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.
- e0 does not have a CSS profile.
- 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!
- Avoid duplication
- Use HTML vocabularies wherever possible
- Make life easier for the content creator, even if that makes life harder for the reading system developer