<itemvalue="A type representing values that are either `Future<T>` or `T`. This class declaration is a public stand-in for an internal future-or-value generic type, which is not a class type. References to this class are resolved to the internal type. It is a compile-time error for any class to extend, mix in or implement `FutureOr`."/>
<itemvalue="A type representing values that are either `Future<T>` or `T`. This class declaration is a public stand-in for an internal future-or-value generic type, which is not a class type. References to this class are resolved to the internal type. It is a compile-time error for any class to extend, mix in or implement `FutureOr`."/>
<itemvalue="An AST visitor that will recursively visit all of the nodes in an AST structure. For example, using an instance of this class to visit a [Block] will also cause all of the statements in the block to be visited. Subclasses that override a visit method must either invoke the overridden visit method or must explicitly ask the visited node to visit its children. Failure to do so will cause the children of the visited node to not be visited. Clients may extend this class."/>