Yes, the regex is $[Address]
The datatype of the source column (Address) is varchar(100), is not nullable and is being populated by the Address Line (Street Number) generator.
The datatype of the destination column is varchar(1000), not nullable and is being populated by the Regex expression which contains $[Address].
BTW, I have also noticed that adding a FK column to the regex window causes this column in the preview pane to gray out and display what appears to be a lock icon - looks like a link of a chain. Is this expected behavior?