ReviewUI subclaseses can now define a is_enabled_for() function, which

returns whether it can be enabled for the given user, review request,

and/or file attachment. This allows, for instance, limiting a review UI

based on extra_data on an object, or based on the given user or

Local Site, or anything else.

Tested this with a file attachment returning True, and then returning False.
Implemented a custom version and tested by file attachment name.