One of the themes of YUIConf 2012 was that YUI is a robust platform to build upon and extend. This is precisely what the folks in the Yahoo! mobile e-commerce team did with Bottle. After you check out the video below, be sure to take a look at their code and give it a try yourself. You can watch all of the released videos from YUIConf 2012 on YUI Theater or YouTube.
In this YUIConf 2012 talk, Montie Tsai and Zordius Chen, Yahoo! mobile e-commerce engineers, discuss a mobile UI library called Bottle that features components packaged as YUI widgets for better reusability. The library is available in the YUI Gallery.
A copy of the slides for this talk can be found on SlideShare (To skip the embedded video, go to the second slide).