Filemaker is supposed to handle null $$ vars by not storing them at all, but if you define a $$var and then clear it in the Data Viewer, it still persists!

Can't think of a possible use for this, but I thought it was interesting.

Not what I see - can you provide a step-by-step?

Create a script that has: Set Variable[$$var; "ABC"]

Run that script.

Confirm that $$var = ABC in your Data Viewer under the "Current" tab.

Double click on $$var and delete its contents.

$$var persists in the "Current" tab for the length of the session in my FMP 11A v1.

Double click on $$var and delete its contents.

Ah, I see. I guess that goes directly inside the value "cell", bypassing any evaluation - incl. variables management.