Where there is a strong justification for using remote resources or non-core media, EPUB supports a fallback option that allows something else that is supported to be displayed in its place. This functionality should be used in these instances.
These guidelines may also be relevant when considering use of non-core media types:
- 29 - Consider a preservation-specific version of the EPUB
- 41 - Harvesting the content of iframes may have unpredictable outcomes