How to merge Designer and XAML editors in one window in Visual Studio?

How to merge Designer and XAML editors in one window (designer on top of xaml editor) in Visual Studi开发者_开发百科o 2010 when working with WPF project?

Currently, to switch between them I need to use tabs.

Click the toggle button in the picture below.

There are three tabs above the output toolbar: "Design", an image with two arrows and "XAML". Click on the image (the second tab). In that way, you can switch - if you want the code to be above or under the design editor.