Sleeve. What is the closest approximation of a sleeve in poetry?

Perhaps, a dust jacket for a hard cover volume. Less & less frequent.
Or the line break; you wonder what will issue forth. Some finished. Some raggedy.


Sleeves in the good meal? Romaine sleeves stuffed with a vegetable pesto & cheese & nuts. Or chicken well spiced. I'll take under advisement with the haiku the cat. A great source of the non sequitur.