What are the differences between EPUB2 and EPUB3? Which is most popular?
According to this page, EPUB3 adds, changes or improves:
- Added HTML5 support
- SVG documents can now appear in the spine in EPUB 3
- Support for MathML
- Semantic Inflection
- Content switching has been simplified by having its processing model defined so that it does not require document preprocessing
- Added modules from CSS3
- EPUB 3 requires Reading Systems to support the OpenType and WOFF font formats for embedded fonts in conjunction with the CSS @font-face rules.
- Audio and video
- Media overlays
- Publication Metadata and Identity
- Resource Metadata
- Manifest Fallbacks
- Remote Resources
- Whitespace in MIMETYPE file
- Disallowed characters in OCF list has been extended
Things that have been removed:
- Out-of-Line XML Islands
- Filesystem Container
- 2.0.1 meta element
From a production standpoint, there aren't really that many differences at a bare-bones level--there's the switch from toc.ncx to toc.xhtml to provide navigational information, a few new metadata elements required in the content.opf file (like
dc:terms modified, which indicates when the file was last modified), and a new header to use. While you can leave out the old toc.ncx and still get a valid epub 3.0 file, for backwards compatability it's best practice to include both toc files--epub 3 readers will ignore the old one, and epub 2 readers will ignore the new one.
As far as bells and whistles go, there are some neat new things: HTML 5 support, including things like
<audio>. Fixed Layout is a pretty big deal, of course. MathML is great if you're doing anything that involves equations, and you can use epub:type to include semantic information that reading systems can do some neat things with (like the popup footnotes in iBooks).