@SubtypeOf(value=UnknownVal.class)
 @Retention(value=RUNTIME)
 @Target(value={TYPE_PARAMETER,TYPE_USE})
public @interface StringVal
An annotation indicating the possible values for a String type. If an expression's type has this
 annotation, then at run time, the expression evaluates to one of the annotation's arguments.
- See the Checker Framework Manual:
- Constant Value Checker