Because the fixed layout EPUB3 format is based on the latest web standards of HTML5, CSS3 and JavaScript it means that other pieces of web code written using these same languages are already compliant with the standard.

To pass EPUB validation the web code used must work offline and not contain references to external resources.

You don’t have to be a coder to create extra web code. We support code made by third party tools such BookWidgets, Tumult Hype, Adobe HTML5 animation apps, or virtually any other source including sharing sites like Codepen.

A widget is a local package of web code used on the Mac and with iBooks Author. CircularFLO allows widgets to be added to the InDesign page and exported out to fixed layout EPUB. 

Web code will be scaled to fit the placeholder frame. There is no requirement to design the web code to a specific pixel dimensions although if using pixel graphics it may be recommended. 

Just like a regular image link you are free to edit the code files outside of InDesign. The latest up-to-date version of the linked files will be incorporated into the ebook.