https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/ranges

var array = new int[] { 1, 2, 3, 4, 5 };
var thirdItem = array[2];    // array[2]
var lastItem = array[^1];    // array[new Index(1, fromEnd: true)]

var slice1 = array[2..^3];    // array[new Range(2, new Index(3, fromEnd: true))]
var slice2 = array[..^3];     // array[Range.EndAt(new Index(3, fromEnd: true))]
var slice3 = array[2..];      // array[Range.StartAt(2)]
var slice4 = array[..];       // array[Range.All]