Code (C++)

public MainWindow()
{
    InitializeComponent();

    var shapeNode = new ShapeNode()
    {
        Shape = new Shape(new ElementTemplate[]
        {
            new LineTemplate(0, 0, 100, 0),
            new LineTemplate(100, 0, 100, 100),
            new LineTemplate(100, 100, 0, 100),
        }, FillRule.EvenOdd),
    };

    shapeNode.AddLabel(new NodeLabel() { Text = "Label - 1" });

    diagram.Nodes.Add(shapeNode);
    diagram.Nodes.First().Move(50, 50);
}

private void diagram_DoubleClicked(object sender, DiagramEventArgs e)
{
    SvgExporter svgExporter = new SvgExporter();
    svgExporter.Export(diagram, @"D:\temp\diagram.svg");
}