Flowing Books: Text Alignment
If specifying line-height, extra spacing between text blocks should be a multiple of the specified line-height to keep text aligned across the spine. See Alignment.
Flowing Books: Tables
In flowing books, iBooks sizes large tables to fit within the width of the page. When a reader double taps the table, the table will open in a new web view that overlays the book. In this web view, the reader can pan and zoom in on the table.
Flowing Books: Spine Items
If the <spine> references a PDF, the linear attribute must be set to no. If the linear attribute is set to yes, delivery will fail.
CSS Styles
If you define CSS styles inline using a <style> tag in the XHTML document, note the following changes. In iOS 5, HTML comments in an XHTML document will always be treated as comments, even if they appear in inline CSS. This behavior is compliant to XHTML standards. Previously, HTML comments within a style tag were ignored, thus applying the style within them, but beginning in iOS 5, <style> nested within <!--> will be ignored. Verify your books and correct if necessary.
Image Alt Attribute Clarification
For accessibility, the alt attribute for an image must be included. To read best practices on using the alt attribute, see Interior Image Requirements.
Fixed-Layout Books: Best Practices
When developing fixed-layout books, you may notice that iBooks sometimes remembers the appearance of your book even after it has been deleted and replaced with an updated version. This is due to caching. If you anticipate making a number of revisions to your books while editing, Apple recommends that you use the Book Proofer app (note: as of October 2014, iBooks for OS X Yosemite or later includes a book proofing tool). Another option is to include the edition's date in the metadata of the OPF. Changing this date will circumvent iBooks' caching.
A fixed-layout book must include a <reference> of type="text" In the <guide> block of the .opf file.
Read Aloud Books
If a Read Aloud Book includes audio or video files in addition to the read aloud narration, you can include the pause-readaloud attribute (or data-pause-readaloud if using iBooks JS) on the <audio> or <video> element. The namespace must be set to http://apple.com/ibooks/html-extensions and pause-readaloud to "true". Using this attribute requires iBooks 1.5. See Embedding Read Aloud Controls for more information.
Books with JavaScript Interactivity
A new section describing delivery requirements and best practices for books with interactive content has been added.
Adobe Creative Suite 5.5 Error
Adobe Creative Suite 5.5 has a bug that may result in XHTML errors in EPUBs exported by InDesign. See Book Validation for details.