It's clearly visible in the code that this is not implemented completely.
The codeof MouseInput looks always like the following:
`boolean isPopupTrigger = false; // TODO`

Should be relevant for unit tests and all the other cases where monocle is used.
It was found in combination with JPro, because JPro also uses Monocle. (https://github.com/JPro-one/JPro-tickets/issues/95)

Simple test:
```
public class MonocleIsPopupTrigger extends Application {

    public static void main(String[] args)
    {
        launch(args);
    }

    @Override
    public void start(Stage stage)
    {
        System.out.println(ClassLoader.getSystemClassLoader());
        System.out.println(ClassLoader.getSystemClassLoader().getParent());
        System.out.println(Scene.class.getClassLoader());
        System.out.println(getClass().getClassLoader());
        Label label = new Label("Hello JPro!");
        label.setOnMousePressed((e) -> {
            System.out.println(e.getButton());
            System.out.println(e.isPopupTrigger());
        });
        label.setOnContextMenuRequested((e) -> {
            System.out.println(e);
        });
        label.setFont(new Font(50));
        label.setAlignment(Pos.CENTER);
        stage.setScene(new Scene(label));
        stage.show();
    }
}
```