Add a way to get:

• Item name
• Item icon name
• Item value in coppers
• Item weight
• Item quality (1 to 8)

By using the itemID.

Also a way to read all those values through an "item use".
Instead of effect("item_use", args, [slot number]) something like effect("item_id", args, [slot number]) which would return the itemID and allows to use the previous operands.

Also:

• A way to know the number of free slots in the main inventory.

To add more details again.

Not having those functions means I have to store the ID inside the object itself. And then a copy of the data somewhere in the campaign.

For an item it's fine, when I have fifty of them, the accumulated texts that duplicate the already stored information starts to account for a lot of data needed to be transferred during the trade of an item. By being careful about the size of everything, for a project of 35kb~ serialized with the quick export, there is 5kb of duplicated text that could be removed. And that's actually a lot when you consider trading 35kb of data through the in game trade windows takes a minute.

To add more details on this, some containers need to interact with the items inside them (inner items or not) and if players aren't careful they can stash the wrong sort of item, or stash them in the wrong order. Having a way to recover the itemID before use allows for more complex items than the basic Simple Rifle provided as example.

Recovering the rest of the info allows even for displaying the items neatly in a dynamic document.