number - The bag id, where the item to use is located
slot
number - The slot in the bag, where the item to use is located
target
string? : UnitId - The unit the item should be used on. If omitted, defaults to "target" if a the item must target someone.
reagentBankAccessible
boolean? - This indicates, for cases where no target is given, if the item reagent bank is accessible (so bank frame is shown and switched to the reagent bank tab).
Details[]
Slots in the bags are listed from left to right, top to bottom. A 16 slot bag has the following slot numbers:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A 6 slot bag has the following slot numbers:
1
2
3
4
5
6
This function is protected, though may still be called in the following situations:
When the (Guild/Reagent) Bank is open: Move the item to/from the (Guild/Reagent) Bank.
When the Merchant frame is open: Sell the item.
When the Mail frame is open and on the "Send Mail" tab: Add the item to the attachments.
When the item is equippable: Equip the item.
When the slot is empty: Do nothing.
When the item is a locked Lockbox: Show an error message that says it's locked.
When the item is a container (Clam Shell, Unlocked Lockbox, etc.): Open the Loot frame and show the contents.
When the item is a book: Open the book's Gossip frame for reading.
When the item is not a usable item: Do nothing.
When the item starts a quest: Open the quest Gossip frame for reading.
When the Trade frame is open: Add the item to the list of items to be traded. (I have not confirmed this)
When the Auctions tab is open: Add item for auction pricing and submission.