Apple Books has several viewing themes that the reader can select for flowing books. These include Book, Full Screen, and Scroll. The Scroll theme scrolls vertically for books with horizontal text, and scrolls horizontally for books with vertical text. This ensures an unbroken/unpaginated text flow.
By default, Japanese and Chinese books scroll horizontally, while all other languages scroll vertically. To redefine the scroll direction, the book must include the following metadata in the .opf file: "ibooks:scroll-axis". Possible values are vertical, horizontal, and default. For example:
<metadata>. . .<meta property="ibooks:scroll-axis">vertical</meta>. . .</metadata>This example is appropriate for a book with horizontal Japanese or Chinese text. When rendered with Apple Books' Scroll theme, horizontal text is most easily read scrolling top to bottom on the vertical axis.