iBooks Link Format
In a book made using iBooks Author, you can link from an HTML widget to another place within the same book, or you can link to an EPUB (.epub) book or to another Multi-Touch (.ibooks) book. When linking to a Multi-Touch book, you can link to a specific location, such as a figure, chapter, section, or page number. See Links for more information.
Book Proofing
iBooks for OS X Yosemite or later includes a book proofing feature that lets you know how your EPUB will look in iBooks to your readers. Once you have your proof set up on your Mac and iOS device, changes you make to your EPUB will update automatically in iBooks on your Mac and any iOS device you have synced. Use this to make sure everything looks and works to your satisfaction before you distribute your book or submit it for sale.
MathML Clarification
The sentence “In addition to the features listed above, MathML is also supported” has been changed to “In addition to the features listed above, presentational MathML is also supported.”