title: Setting design time DataContext on a Window is giving a compiler error?
body: <p>I have the following XAML below for the main window in my WPF application, I am trying to set the design time <code>d:DataContext</code> below, which I can successfully do for all my various UserControls, but it gives me this error when I try to do it on the window...</p>
  
  <p><code>Error  1   The property 'DataContext' must be in the default namespace or in the element namespace 'http://schemas.microsoft.com/winfx/2006/xaml/presentation'. Line 8 Position 9. C:\dev\bplus\PMT\src\UI\MainWindow.xaml 8   9   UI</code></p>
  
  <pre><code>&lt;Window x:Class="BenchmarkPlus.PMT.UI.MainWindow"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:UI="clr-namespace:BenchmarkPlus.PMT.UI"
      xmlns:Controls="clr-namespace:BenchmarkPlus.PMT.UI.Controls"
      d:DataContext="{d:DesignInstance Type=UI:MainViewModel, IsDesignTimeCreatable=True}"
      Title="MainWindow" Height="1000" Width="1600" Background="#FF7A7C82"&gt;
  
      &lt;Grid&gt;
          &lt;!-- Content Here --&gt;
      &lt;/grid&gt;
  
  &lt;/Window&gt;
  </code></pre>