Yes, it's even the default behaviour (at least on Linux). What is the problem?

Qt Code: 
  1. #include <QtGui>
  2. #include <QDebug>
  3.  
  4. class MainWindow: public QMainWindow {
  5.     Q_OBJECT
  6. public:
  7.     MainWindow(QWidget *p = 0): QMainWindow(p) {
  8.         setGeometry(0, 0, 640, 480);
  9.  
  10.         setDockNestingEnabled(true);
  11.         QDockWidget *dock1 = new QDockWidget(tr("Dock 1"), this);
  12.         dock1->setAllowedAreas(Qt::AllDockWidgetAreas);
  13.         QDockWidget *dock2 = new QDockWidget(tr("Dock 2"), this);
  14.         dock2->setAllowedAreas(Qt::AllDockWidgetAreas);
  15.         QDockWidget *dock3 = new QDockWidget(tr("Dock 3"), this);
  16.         dock3->setAllowedAreas(Qt::AllDockWidgetAreas);
  17.         addDockWidget(Qt::TopDockWidgetArea, dock1);
  18.         addDockWidget(Qt::TopDockWidgetArea, dock2);
  19.         addDockWidget(Qt::TopDockWidgetArea, dock3);
  20.         // No central widget
  21.     }
  22. public slots:
  23. private:
  24. };
  25.  
  26. int main(int argc, char *argv[])
  27. {
  28.     QApplication app(argc, argv);
  29.  
  30.     MainWindow m;
  31.     m.show();
  32.     return app.exec();
  33. }
  34. #include "main.moc"
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