title: Why does Blend add [d:LayoutOverrides="Height"] and should I care?
body: <p>Quite often when coming back to Visual Studio from Expression Blend 3, I see that Blend has helpfully added a "d:LayoutOverrides" property to my XAML. Growing up with ASP.NET designers, I naturally distrust anything I wouldn't type myself, so remove them as soon as I see them. </p>
  
  <p>I know that "d:" properties are designer-only and don't impact runtime, but can anyone offer any insight into what this property does and why Blend would be so insistent that I have them all over my markup?  </p>
  
  <pre><code>&lt;Border d:LayoutOverrides="Height" /&gt;
  </code></pre>