https://learn.microsoft.com/en-us/dotnet/api/system.runtime....
Examples of usage:
- https://github.com/U8String/U8String/blob/main/Sources/U8Str...
- https://github.com/nietras/1brc.cs/blob/main/src/Brc/BrcAccu...
- https://github.com/dotnet/runtime/blob/main/src/libraries/Sy...
(and many more if you search github for the uses of Vector128/256<byte> and the like!)