But what is a Descriptor Unit?

Gosh, I thought I knew. The DescriptorUnit defines behavior. So its kinda like the type of Topic. And that probably works for a lot of things, but now I'm looking at access controls.

Is the "owner" of a topic a descriptor? I think so.

Now access controls may be based on type in many cases. For example, only the owner of a Remark can change it.

So, perhaps I just need to specify the owner and a "common" DescriptorUnit. I'm not sure.

I think know Norm's answer--every Topic should likely have its own DU.