Use by holding left-ALT and click the item you want to show while having the chat or PM open.
If it doesn't work in PM, try to make the PM box larger. Clicking the bottom-right corner of the PM box allows you to adjust the size.
If it was used, the item will appear in a chat like this: [Sword +9]. When you click the item, you get a precise list of the item's details. If the item has bonuses, it will appear yellow instead.