Hi,
There are a large number of widgets that have been added into the Alfresco Community source that are in varying stages of completion. The general rule of thumb should be that if they are used by default in 4.2 then they're "safe" to be used, but if not then they should be considered "beta" and as such functions, variable names, capabilities are subject to change and there is also no guarantee that the widgets are even completely functional. We were working on a new version of the Document Library for 4.2 but made a decision based around available time and resources required to achieve feature parity with the existing YUI2 based Document Library and decided that we would postpone the work for a future release. However, the widgets have been left in the source to give an indication of the direction in which we're heading. I would certainly not recommend using any of these widgets in production systems and I'm very deliberately *not* going to be answering specific questions on how you can use them (since there is a high probability that the information will become out-of-date almost immediately).
I will be demonstrating some of these widgets in action at Summit next month with a detailed explanation of what we're up to and what can be expected in the future. If you're not going to Summit then I'm reasonably confident that videos of the sessions will appear online at some point in the future (although I can't say when)
Regards,
Dave