A great intro by Nick
List patterns - C# 11.0 draft specifications
Lets you to match an array or a list with a sequence of patterns e.g. array is [1, 2, 3] will match an integer array of the length three with 1, 2, 3 as its elements, respectively. The pattern syntax is modified as follow: list_pattern_clause : '[' (pattern (',' pattern)* ','?)?