Because Apple Books scales the book to fit within the viewport, both landscape-dominant and portrait-dominant books will maintain their intended layout in either orientation of the device, even after an orientation change.
Readers can choose to read the book at the zoom-level that is most comfortable for them.
When developing fixed-layout books, you may notice that Apple Books 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, you can modify metadata in the package document (.opf file) to iterate the date-modified metadata. For example:
<metadata xmlns="http://www.idpf.org/2007/opf" xmlns:dc="http://purl.org/dc/elements/1.1/"> <dc:title>Fixed-Layout Example 3.2</dc:title> <dc:identifier id="bookid">0123456789</dc:identifier> <dc:language>en</dc:language> <meta property="dcterms:modified">2012-08-15T00:00:00Z</meta> </metadata>