title: Error "Tag does not exist in XML namespace"
body: <p>To illustrate the issue, I have created a simple sample project where I am getting compilation errors on the XAML definition.</p>
  
  <p><strong>Here is my class definition:</strong></p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Threading.Tasks;
  
  namespace MVVMTest.Foo
  {
      public class FooTestClass
      {
          public String Name { get; set; }
  
          public String Key { get; set; }
      }
  }
  </code></pre>
  
  <p>It should be noted that FooTestClass resides in the Foo subfolder (of the MVVMTest folder)</p>
  
  <p><strong>Here is my XAML:</strong></p>
  
  <pre><code>&lt;Window x:Class="MVVMTest.MainWindow"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
          xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
          xmlns:local="clr-namespace:MVVMTest"
          xmlns:mView="clr-namespace:MVVMTest.Foo;assembly=MVVMTest"
          mc:Ignorable="d"
          Title="MainWindow" Height="350" Width="525"&gt;
  
      &lt;Window.Resources&gt;
          &lt;mView:FooTestClass x:Key="ddd" /&gt;           
      &lt;/Window.Resources&gt;
      &lt;Grid&gt;
      &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>I'm getting the following error message</p>
  
  <blockquote>
    <p>The tag 'FooTestClass' does not exist in XML namespace
    'clr-namespace:MVVMTest.Foo;assembly=MVVMTest'. Line 12 Position 10.<br>
    MVVMTest      C:\Dev Projects\MVVMTest\MVVMTest\MainWindow.xaml      </p>
  </blockquote>
  
  <p>Is there an issue in VS?</p>