LibItemInfo is a library of functions used to aid in the gathering of item information. Each function can be called passing in a (bagId, slotId) or a (Link). I wrote it for use in my JunkIt addon which needed to handle both inventory items by (bagId, slotId) and lootable items in loot windows by (links).
There are several functions designed to gather research, crafting, & trait information. Some are used to figure out what type of item you have: Is it a glyph, one-handed or two-handed weapon, jewelry, ect.. Some mimic built in functions, but were written so I did not need to constantly write code everywhere to first check & see if I had a (bagId, slotId) or a link. That and when I wrote it (and JunkIt) we did not have all of the GetItemLink API that is available today.