What feature does a playwithin-a-play involve?

A play-within-a-play is a theatrical device where a story is presented as part of another story. This feature allows playwrights to explore themes, provide commentary, or develop character relationships in a layered manner. By including a separate performance within the main narrative, the playwright can enhance the audience's understanding of the primary storyline, often reflecting on the events and themes presented in the main play. This technique can create a richer experience for the audience, as they engage with both the primary and secondary narratives simultaneously.

In contrast, the other options do not accurately describe the nature of a play-within-a-play. Multiple roles performed by a single actor, storytelling through poetry, and musical interludes do not encapsulate the essence of the layered storytelling approach that defines a play-within-a-play.