What is the new "and" keyword in C#?

I was just writing C# code and intellisense gave me a suggestion for the "and" keyword.

    if (context.Request.Parameters[0] is string operationType and )

In the above snippet the "and" in the end was suggested. Selecting it caused the following error to pop-up.

Error CS8652 The feature 'and pattern' is currently in Preview and unsupported.

My main question is where I can find the documentation for this feature?