Foreign Resources may be included in an EPUB Publication without a fallback provided they are not referenced from spine itemref elements [Packages 3.1] or directly rendered in their native format in EPUB Content Documents (e.g., via [HTML] embedded content and [SVG] image and foreignObject elements). (idpf.org)
The rendition: spread - landscape, rendition: spread - both, rendition: spread - auto and rendition: spread - none properties [Rendition Vocab] may be specified locally on spine itemref elements, and will, in such cases, override the global value for the given spine item. (idpf.org)
Values can be specified in OPF through «properties» attribute in itemref tag. (wiki.mobileread.com)