Currently all custom fonts included in AMP documents are subject to the browser's default loading behavior.

Since there is only a single heuristic for all fonts, it cannot be good in all cases.

There are two primary types of fonts:

1. Logo fonts. You'd never want FOUT (unstyle text) with these, but FOIT (invisible text) would be fine
2. Content fonts. Here various different behaviors may be desirable:
   • Timeout after which fallback font is shown
   • FOUT
   • I'd argue that FOIT is not good in this case.

Whatever the solution is to achieve these goals, it should ideally not require a JavaScript download to initiate the font request.