It's straight forward:
Since June 2015 vaadin also supports their own Font Icons: Vaadin Font Icons.
In our JVx' VaadinUI, it wasn't possible to use FontIcons without accessing the real vaadin resource, e.g.
With next release, we'll allow FontAwesome and VaadinIcons out-of-the-box, without accessing the ressource and without manual installation of font icons, because our UI has everything included.
It will be possible to write:
This feature is not official because it's not technology independent, but it's already available in our nightly builds