As shown by https://github.com/enyojs/bootplate/blob/master/source/package.js (line 3) we must reference "$lib/onyx/source" in our package.js.

It's seems that it's to avoid loading "onyx/css" directory content.
I'm not sure to understand everthing here.
@opopova : could you have a look and tell us what should be included into Ares package.js ?