Droppables can now be configured with an 'accept' option; a selector string or a function against which to test the original draggable DOM element. Returning true (or matching the selector) permits drop interaction.
Making the examples/fixtures slightly more sane.
Moved the draggable spec options up a scope-level.
Draggables can now be configured with a 'stack' option; a selector string or a function that returns a jQuery collection, or a collection of DOM elements. The draggable will always stay on top (z-index-wise)  of the stack represented by that collection (or matching the selector).
No need to run this test again.
Changed my mind; the helper factory function should receive the jQuery object representing the draggable as its first parameter. This is a jQuery plugin, after all.