The texture variable will contain the item's texture and the itemCount variable will contain the number of that item in the slot.
The quality return value will either be -1 or a standard quality value from 0 to 6. A value of -1 seems to indicate that the item requires special handling: It's stackable, it's unique or it's a quest item.
The readable return value simply indicates if there is text related to the item. If it's true, the default UI will change the cursor to the "Read" cursor (the magnifying glass) when the mouse is over the item button.
An item in a character's inventory can become "locked" for a number of reasons. It might be locked because it is attached to the cursor, or because it has been split and the new stack is attached to the cursor, or because is in the "create auction" item slot, or because it is in a trade slot. In all of these cases, the item is considered to be "locked". Also, typically, the item's icon is shown in grayscale. The item will become unlocked when the action that locked the icon is complete. When the item's move is finished (and the server accepts the move), the item will become unlocked. When the server reports that the auction has been created, the item will become unlocked (although it will also disappear). During the period that the item is locked, some methods that affect the item (such as PickupContainerItem) silently fail.