Add option for specifying the element dragged elements should be appended to.

The specified element is what elements will be appended to while they are being dragged. If not specified they will remain where they were in the DOM and just be positioned relative to their offset parent.

This is helpful if, for example, you want dragging elements to be pulled up to be children of the body tag so that they are guaranteed to appear on top of all other elements. If we leave them as children of whatever their container was there is the possibility that another element may have a higher z-index due to the way z-indexes interface with stacking contexts (see https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Understanding_z_index/The_stacking_context).
Switch to using data attributes for specifying that elements are draggable.
Switch to using tabs for indentation.