It seems like we should be developing using the alpha branch, but the docs point to the master branch, so there are some inconsistencies. E.g. the alpha branch of DragTarget's LongPressDraggable doesn't have a onDragCompleted callback (https://github.com/flutter/flutter/blob/alpha/packages/flutter/lib/src/widgets/drag_target.dart#L219) whereas the docs say that it is a constructor property (https://docs.flutter.io/flutter/widgets/LongPressDraggable-class.html).