The EPUB3 format has been documented in the open since 2010, but Amazon hasn't seen fit to implement it on the Kindle. Instead, Amazon uses a proprietary version of the MOBI format. Since the Kindle is such a dominant force in electronic books, the whole e-Book market is being held back. As I pointed out the other day, e-Reader innovation hasn't stalled, the public is prevented from enjoying the advances which have occurred, because of Amazon's actions. Amazon doesn't say why they've done this.