| Condition         | Result       |
|-------------------|--------------|
| "test" is String  | true         |
| "test" is String? | true         |
| null is String    | false        |
| null is String?   | true         |
|                   |              |
| "test" as String  | ok           |
| "test" as String? | ok           |
| 123 as String     | throw        |
| 123 as String?    | throw        |
| null as String    | throw        |
| null as String?   | returns null |
| null as? String   | returns null |
| null as? String?  | returns null |