To keep up with the newly (I think it's new...) added feature wherein a player may scroll while hovering over a bundle to select a specific stack to pick up from within, it is important that there be some way to access the index of the itemstack being selected, upon pickup.

A field in InventoryClickEvent would likely do the job. I'm not well-versed in how exactly the client communicates the chosen item, and how Bukkit/Spigot handles calling the event from there. But I assume, in my ignorance, that providing the index of the selected item would be of little effort.

Something like InventoryClickEvent.getBundleSlot() would be quite perfect.

This isn't, by any means, a high priority feature, but I'm not much of an NMS enjoyer, and it would make Bukkit/Spigot's API more complete.

(Attached is an image depicting the scroll-selection process)