Does draggable's stack option have to be a complex hash?

Does draggable's stack option have to be a complex hash?

I was taking a look at the Draggable dosc and saw the stack option:
stack
<a href="http://docs.jquery.com/UI/API/1.7/Draggable#option-stack">http://docs.jquery.com/UI/API/1.7/Draggable#option-stack</a>
"Controls the z-Index of the defined group (key 'group' in the hash,
accepts jQuery selector) automatically, always brings to front the
dragged item. Very useful in things like window managers. Optionally, a
'min' key can be set, so the zIndex cannot go below that value."
Code example:
$('.selector').draggable({ stack: { group: 'products', min: 50 } });
What is the need for a user having to specify a min option? Imagine you have 3 elements that are all stacking together. I'm can see them either swapping three z-Index values around as you drag them:
100, 101, 102
100, 102, 101
102, 101, 100
or increasing each time
100, 101, 102
100, 103, 102
104, 103, 102
But I'm trying to imagine a scenario where the z-Index would decrease, then requiring the user to specify a min. Also, what's the expected behavior if the user doesn't specify a min, as the default value for stack is false?
Without this stack.min, could this option be a simple string instead of a hash? Like so
$('.selector').draggable({ stack: 'products' });
but that also makes me think, why isn't this a selector, instead of a group name? Then you could even specify stack: true which could be equivalent to stack: '.ui-draggable'. This would be consistent with the snap option:
snap
<a href="http://docs.jquery.com/UI/API/1.7/Draggable#option-snap">http://docs.jquery.com/UI/API/1.7/Draggable#option-snap</a>
"If set to a selector or to true (equivalent to '.ui-draggable'), the
draggable will snap to the edges of the selected elements when near an
edge of the element."
Thoughts?
- Richard