Uranium is only 15KB when zipped. This makes it perfect for mobile devices, where minimizing KB is essential. It's also possible to make a custom build if you need it to be even lighter.
Uranium makes the view (your UI/UX) rely on the model (your HTML). The declarative aspect is not designed for performing functions. You wouldn't want to add attributes to an element to perform some js logic (this is exactly why 'onclicks' should be avoided) - thats what events/listeners/callbacks are for.
Sean is the lead architect on Uranium - core design and philosophy.. He's the guy to go to for most Uranium questions.
Hampton helped with the core design and philosophy of Uranium.
Jeff created the awesome geocode widget, which allows you to reverse-geocode a user's location. The information gained is then used to populate a form.
Sam has also contributed to the select list widget.
Aaron coded the beautiful thing that is font resizer. It pretty much does what you expect: allows you to easily resize text at the click of a button.
Here's more information on the Uranium project. It's not essential for a beginner, but you may want to check this stuff out if you become more interested in Uranium.