From the (San Francisco Mid-Peninsula) Daily Post of 8/14/14, p. 1, “Massage parlor workers arrested”:
Redwood City police conducted an undercover operation at the Aurora Spa at 1865 Broadway on July 22 after receiving complaints of illegal prostitution.
Not just prostitution, but illegal prostitution. But prostitution is in fact illegal in California (and other places outside of Nevada), so what is the adjective illegal doing here?
This is an appositive, rather than restrictive, use of the adjective — a phenomenon I’ve posted about several times, at greatest length in a 2/8/07 Language Log posting “Droning on”, about the expression pilotless drones.