A stoop in Queens. Passionate opinions on music. A spontaneous rap battle. The Purists is by up-and-coming playwright Dan McCabe, who has a deep feeling for real people and how they really talk. The play’s quintet of actors is directed by already-there-and-then-some Billy Porter (Kinky Boots, “Pose”). This world premiere won raves and has been extended by popular demand. —L.J.