External xhtml files are not supported by any epub. Epub3 does support external audio and video resources. Also only EPub3 supports javascript and not all e-readers allow it. Javascripts should be defined in head inside a script tag.
Sigil also has Preferences that determine if javascript is allowed and if access to external resources is allowed.
You might want to think about if an iframe might be what you want pointing to each of your external resources.
Last edited by KevinH; 03-19-2021 at 06:08 PM.
|