Draggable: stack option resets the z-index

[janesconference]

*test case here*: ​http://jsfiddle.net/gwDXP/2/

This bug is observed when one's using draggables with the stack option activated, like in:

$( ".plugin" ).draggable({cursor: "move", opacity: 0.9, stack: ".plugin", scroll: true});

Problem: When one of the divs gets dragged, its z-index is reset to 1 (and incremented each time it is sent to the top, because of the stack option).

Desidered behaviour: The div z-index should start from the original z-index value for the .plugin divs (200, in the linked test case) and be incremented from that value.

Additional details: Jquery-ui 1.7 had a min parameter for the stack option.

In newer versions of jquery-ui (1.9.2 to 1.10 is affected, for instance), you can only specify a selector, and, from which I can understand, the stacking should start from the pre-existent z-index of the element. Instead, it seems arbitrarily re-starting at 1.

[tj.vantoll]

See #4365 for discussion of the hash for the stack option being removed.

It looks like the min is *supposed* to be the z-index of the first element matching the selector - ​https://github.com/jquery/jquery-ui/blob/master/ui/jquery.ui.draggable.js#L920. That indeed does not appear to be working.

[tj.vantoll]

Pull request: ​https://github.com/jquery/jquery-ui/pull/913.

[TJ VanToll]

Draggable: Account for z-index set in CSS for the stack option. Fixed #9077 - Draggable: stack option resets the z-index

Changeset: c32bebd1bd28d158b017bb1dd7f95fb1d8a8d567