TIWCGJQTreeViewUIPlugin.SelectMultipleModifier Property
The special key used to make a click add to the selection and not replace it ("ctrl", "shift", "alt", "meta"). You can also set this to "on" making every click add to the selection.
published property SelectMultipleModifier: TIWCGJQTreeViewKeys index 01 read GetSelectMultipleModifier write SetSelectMultipleModifier stored IsEnumerStored;