() make the left hand side a list. Arrays return their elements when evaluated in list context.

See also perldata :

Assignment is a little bit special in that it uses its left argument t
+o determine the context for the right argument. Assignment to a scala
+r evaluates the right-hand side in scalar context, while assignment t
+o an array or hash evaluates the righthand side in list context. Assi
+gnment to a list (or slice, which is just a list anyway) also evaluat
+es the righthand side in list context.
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Cheers, Christoph