Images
When sizing interior images in the EPUB, it is recommended to size the container using viewport units to maintain adaptability for various screen sizes. Previous versions of this guide recommended using percentage units. See Interior Image Requirements for examples.
Apple recommends that you set the colorspace on your book images (for both EPUB and Multi-Touch books) to sRGB. This colorspace functions best on hardware, and iBooks Author can best optimize images that use this colorspace.
Embedding Audio and Video
The height and width attributes of embedded audio and video in an EPUB can be defined in either HTML or in the CSS. The height and width attributes have been removed from the HTML examples. See Embedding Audio and Video.
EPUB Proofing
The Safari Web Inspector is an open source web development tool built into Safari that makes it easy to proof your content on OS X. The Web Inspector can be enabled within iBooks on OS X 10.9 (or later). During book development, using this tool allows you to more easily modify, debug, and optimize your book. See Using Safari Web Inspector for more information.
Book Versioning
Books can be either versioned or unversioned. A “versioned book” refers to a book asset that has been revised with a version number. Only EPUB 3 and Multi-Touch books can be versioned. An “unversioned” book is one that has not had a version number assigned and can apply to EPUB 2 and EPUB 3 books.
When you deliver a new book asset for an unversioned book (either EPUB 2 or EPUB 3), you can provide text in the <version_whats_new> tag to explain what has changed in the new version. You do not need to supply a version string unless the asset was previously assigned a version number. See the Apple Books Book Package Specification for information.
Sample assets should not be versioned; however, if you do supply a version number for a sample file, the version number will be ignored. The sample inherits the version number of the book asset.
Schema Version
The version number of this guide has changed from 5.1 to 5.2 to keep the version number in sync with the new schema version.