Which properties can be on a Resource Group Inventory Report?

I made a Resource Group Inventory targeting Customers/!(*/*) to get the host counts for each customer folder, using the convenient built-in or default property host.count, but I would like to put other information about each group as columns.

But the only options that are suggested are system.categories and system.deviceGroupId …. which is weird, and not particularly. But I just forced in columns named name, description, system,displayname, anything I could think of, and those columns all end up blank.

Is there any documentation on what properties work on this report? Or am I missing something obvious?

Thanks!