One of these libraries adds support for specifying a CSS selector for script.aculo.us Sortable containment. It uses Prototype 1.6’s new Function#wrap to add the behavior in an aspect-oriented way without modifying the original Sortable source code. This is the library that powers Backpack’s widget reordering. It’s currently being used in Backpack and Basecamp.
Another library, internally called Hover Observer, uses an unobtrusive technique (monitoring the entire page for mouse movement) to add and remove a “hover” class on element hierarchies with certain class names. Combined with CSS, this allows us to easily show the edit/delete/move “nubbins” when you mouse over widgets on the page, or show drop-down menus when you mouse over applications in Open Bar. The library also lets us specify enter and exit delays, so if you accidentally mouse outside of a target area, the hover class isn’t removed immediately. Think of it as a cross-browser implementation of the :hover CSS pseudo-class, on steroids. Hover Observer was developed for Backpack and is now being used in Basecamp and Highrise.
The last library is tentatively known as Transitions, and provides an extremely simple API for animating transitions between DOM states. The animation resizes and fades an element’s content from one state to another, much like the effect you see when switching preference panes in OS X System Preferences. You’ll see the effect when you edit any item in Backpack. Because the API is simple, RJS-compatible, and easy to integrate into existing applications, we were able to develop it and drop it into Backpack in a single weekend. I’ll post more on this library when it’s ready for public consumption.