What are curly braces { } — CCA-F Exam Prep

Police find a wallet on the sidewalk.
Inside: a driver's license, a credit card, a gym membership, a photo of two kids. Four different items. But the wallet tells the detective one thing immediately: these all belong to the same person.
Now scatter those same items across a city block. A license in a gutter. A credit card on a bench. A gym card in a trash can. Same items. No wallet. Without the container, they're evidence from four different cases.