Introduced in .NET 5, there are new pattern matching operators that can streamline pattern matching. You can now use, and, or, and not in a pattern matching statement

# in an if statement
if (test is not null)
	; // Stuff

public static bool IsLetterOrSeparator(this char c) =>
    c is (>= 'a' and <= 'z') or (>= 'A' and <= 'Z') or '.' or ',';