Comment by gildas

I haven't looked closely, but I get the impression that this is an implementation detail which is not really related to the format. In this case, a polyglot zip/html file could also interrupt page loading via a window.stop() call and rely on range requests (zip.js supports them) to unzip and display the page. This could also be transparent for the user, depending on whether the file is served via HTTP or not. However, I admit that I haven't implemented this mechanism yet.