Final answer:
The audience's seating arrangement around the stage and the use of non-specific character names signify that 'The Box' is avant-garde or experimental theater.
Step-by-step explanation:
The two details that reveal the play titled The Box as an example of avant-garde or contemporary experimental theater are the audience's seating arrangement and the character's namelessness. Firstly, the audience is seated around the stage, which is characteristic of experimental theater spaces such as a Black Box theatre or arena stage, where traditional separation between the performers and spectators is eliminated to create a more intimate and interactive experience. Secondly, the use of PERSON A instead of a proper name evokes the minimalism and abstraction often found in avant-garde performances, as seen in works within the Theatre of the Absurd.